MCCQE Part I medicine: gastroenterology, nephrology & endocrinology questions

Tissue transglutaminase IgA (tTG-IgA) is the recommended first-line serologic test for celiac disease because of its high sensitivity and specificity, but IgA deficiency occurs in about 2-3% of celiac patients and causes a false-negative tTG-IgA, so a total serum IgA level must be checked concurrently. If IgA is deficient, IgG-based testing (deamidated gliadin peptide or tTG-IgG) should be used instead. Patients must continue eating gluten before testing to avoid false-negative results. Confirmatory duodenal biopsy is performed only after positive serology, while the patient remains on a gluten-containing diet.

• B. Fecal fat testing assesses fat malabsorption generally and is not specific for celiac disease.
• C. Genetic testing has high sensitivity but low specificity and is reserved for equivocal cases or to exclude disease, not first-line screening.
• D. Anti-gliadin IgG antibodies have poor sensitivity and specificity and are no longer recommended for screening.
• E. Biopsy is the confirmatory test after positive serology, not the initial investigation.

Rome IV criteria define irritable bowel syndrome as recurrent abdominal pain on average at least one day per week in the last three months, associated with two or more of: relation to defecation, change in stool frequency, or change in stool form, with symptom onset at least six months prior. This patient meets these criteria and has no alarm features such as bleeding, weight loss, nocturnal symptoms, or anemia, so extensive investigation is not required before making the diagnosis. IBS is a clinical diagnosis based on symptom pattern once red flags are excluded. Routine colonoscopy or biopsy is unnecessary in typical presentations without alarm features.

• B. Crohn disease would be expected to show abnormal inflammatory markers, weight loss, or other alarm features, which are absent.
• C. Microscopic colitis typically causes chronic watery diarrhea, often in older patients, and is diagnosed on colonic biopsy, not suggested here.
• D. Celiac disease classically presents with malabsorptive features or positive serology, neither described here.
• E. Lactose intolerance typically causes symptoms temporally related to dairy ingestion, not described in this vignette.

Crohn disease is characterized by transmural, granulomatous inflammation that can affect any part of the gastrointestinal tract from mouth to anus, classically with skip lesions and a predilection for the terminal ileum. Perianal disease, including fistulas and abscesses, is a hallmark extraintestinal complication of Crohn disease and helps distinguish it from ulcerative colitis. Ulcerative colitis, in contrast, involves continuous mucosal (not transmural) inflammation beginning in the rectum and extending proximally without skip lesions or granulomas. The combination of skip lesions, transmural granulomatous inflammation, and perianal disease in this patient is diagnostic of Crohn disease.

• B. Ischemic colitis typically occurs in older patients with vascular risk factors and presents acutely, not with chronic skip lesions and granulomas.
• C. Ulcerative colitis shows continuous mucosal inflammation starting at the rectum, not skip lesions or granulomas, and does not cause perianal fistulas.
• D. Infectious colitis would not characteristically show granulomas or chronic perianal fistulizing disease.
• E. Diverticulitis presents with localized left lower quadrant pain typically in older patients and does not cause granulomatous ileal inflammation.

In acute severe ulcerative colitis, failure to respond to intravenous corticosteroids by day 3 (using criteria such as the Oxford/Travis criteria, e.g., more than 8 stools per day or CRP greater than 45 mg/L with 3-8 stools) indicates a high likelihood of needing colectomy or rescue medical therapy. Rescue therapy with infliximab or cyclosporine is appropriate at this point, with early surgical consultation, because continuing steroids alone risks progression to toxic megacolon, perforation, or death from delayed definitive treatment. Early identification of steroid-refractory disease and timely escalation reduces morbidity and mortality. Loperamide is contraindicated in acute severe colitis because it increases the risk of toxic megacolon.

• A. Oral mesalamine is insufficient for acute severe colitis and is not used as rescue therapy in this setting.
• B. Discharging a patient with ongoing acute severe colitis is unsafe and inappropriate.
• C. Loperamide is contraindicated in acute severe colitis as it can precipitate toxic megacolon.
• E. Continuing steroids alone in a patient meeting criteria for steroid failure delays necessary escalation and increases risk of complications.

Before initiating anti-TNF therapy such as infliximab, patients must be screened for latent tuberculosis using an interferon-gamma release assay (or tuberculin skin test) and for hepatitis B infection with serology, because anti-TNF agents can cause reactivation of both latent TB and hepatitis B, leading to serious or fatal outcomes. If latent TB is identified, treatment should be initiated before or concurrently with biologic therapy. Hepatitis B carriers require antiviral prophylaxis to prevent reactivation during immunosuppression. A chest radiograph alone is insufficient without TB-specific testing, and routine HIV testing is not a standard requirement specific to anti-TNF initiation.

• A. A chest radiograph alone without an interferon-gamma release assay or tuberculin skin test is insufficient to screen for latent TB.
• B. HIV testing is not a routine standard requirement specifically mandated before anti-TNF initiation, unlike TB and hepatitis B screening.
• C. Fecal calprotectin assesses disease activity, not infectious risk before immunosuppression.
• E. Iron studies assess for anemia but are not part of mandatory pre-biologic infection screening.

The Canadian Task Force on Preventive Health Care recommends screening average-risk adults aged 50 to 74 years with fecal immunochemical testing (FIT) every one to two years as the preferred screening strategy, based on evidence of reduced colorectal cancer mortality with an acceptable balance of benefits and harms. Colonoscopy is not recommended as a first-line population screening tool in Canada because of higher cost, invasiveness, and procedural risk compared to FIT, though it remains the follow-up test for a positive FIT result. Guaiac-based fecal occult blood testing has been largely replaced by FIT due to superior sensitivity and specificity. Screening should begin at age 50 in average-risk individuals, not delayed to age 60.

• A. Routine colonoscopy as the primary screening modality is not recommended by the CTFPHC for average-risk adults due to invasiveness and resource considerations.
• C. Guaiac-based testing has lower sensitivity than FIT and is no longer the preferred fecal test.
• D. Annual flexible sigmoidoscopy is not the CTFPHC-recommended interval or primary modality for average-risk screening.
• E. Screening should begin at age 50, not be delayed until age 60, in average-risk adults.

Patients with Lynch syndrome, caused by pathogenic mutations in mismatch repair genes such as MLH1, MSH2, MSH6, or PMS2, have a markedly elevated lifetime risk of colorectal cancer and require colonoscopy every one to two years, typically starting at age 20 to 25 or 2 to 5 years before the youngest affected relative's age at diagnosis, whichever is earlier. This surveillance interval is far more intensive than average-risk population screening because of the accelerated adenoma-to-carcinoma progression seen in Lynch syndrome. Average-risk screening tools such as FIT or extended colonoscopy intervals are inadequate for this high-risk population. Given her mother's diagnosis at age 42, surveillance should already be underway in this 35-year-old patient.

• A. Flexible sigmoidoscopy does not visualize the proximal colon, where Lynch syndrome-associated cancers frequently arise.
• B. FIT every two years starting at 50 reflects average-risk screening and is inadequate for Lynch syndrome's accelerated cancer risk.
• D. A 10-year interval is appropriate only for average-risk individuals, not those with a hereditary cancer syndrome.
• E. CT colonography is not the recommended surveillance modality for Lynch syndrome and does not replace colonoscopy at the needed interval.

Current evidence and guidelines support outpatient management of uncomplicated acute diverticulitis in hemodynamically stable patients who can tolerate oral intake, without routine antibiotic use, because randomized trials have shown no difference in recovery time or complication rates between antibiotic and non-antibiotic management of uncomplicated disease. Management consists of symptomatic treatment with analgesia and dietary advancement as tolerated, with antibiotics reserved for patients who are immunocompromised, septic, or fail to improve. This patient is afebrile, hemodynamically stable, and has uncomplicated disease on imaging, making her an appropriate candidate for outpatient care without antibiotics. Hospitalization and intravenous antibiotics are reserved for complicated diverticulitis or signs of systemic illness.

• A. Surgery is reserved for complicated diverticulitis with abscess, perforation, fistula, or recurrent/refractory disease, not this uncomplicated presentation.
• B. Percutaneous drainage is indicated for diverticulitis complicated by a drainable abscess, which is absent on this patient's CT.
• D. Intravenous antibiotics and hospitalization are reserved for complicated diverticulitis or systemic illness, not present here.
• E. Routine antibiotics are not required for uncomplicated diverticulitis based on current evidence, even in the outpatient setting.

Diverticular bleeding is the most common cause of acute, painless, large-volume lower GI bleeding in elderly patients, typically presenting with sudden hematochezia without preceding abdominal pain. NSAID use, as in this patient, is a recognized risk factor for diverticular hemorrhage because NSAIDs impair mucosal protection and promote vessel injury at the diverticular neck. Bleeding is usually self-limited but can be massive, as suggested by the hemodynamic instability and hemoglobin drop here. Angiodysplasia causes slower, often occult or moderate bleeding rather than this abrupt large-volume presentation, and malignancy typically causes chronic occult blood loss rather than acute hemorrhage.

• A. Angiodysplasia typically causes slow, intermittent, often occult bleeding rather than sudden massive hematochezia.
• C. Hemorrhoids cause bright red blood coating stool or on tissue, not massive bleeding with hemodynamic instability.
• D. Ischemic colitis typically presents with crampy abdominal pain and bloody diarrhea, not painless massive hematochezia.
• E. Colorectal cancer usually causes chronic occult blood loss or iron deficiency anemia rather than acute large-volume bleeding.

Oral vancomycin (or fidaxomicin) is now the recommended first-line treatment for an initial episode of C. difficile infection of any severity, replacing metronidazole as first-line therapy. Vancomycin acts locally within the colonic lumen, achieving high local concentrations with minimal systemic absorption, which is ideal for treating a luminal infection. This patient has non-severe to moderate disease (white cell count below 15 × 10⁹/L, creatinine not significantly elevated) and is clinically stable, so oral vancomycin 125 mg four times daily for 10 days is appropriate. Metronidazole is now reserved for use only when vancomycin or fidaxomicin are unavailable.

• A. Rifaximin is not recommended for initial treatment; it has a role in some recurrent cases as adjunct therapy.
• C. Intravenous vancomycin does not reach the colonic lumen in adequate concentrations and is ineffective for C. difficile colitis.
• D. Intravenous metronidazole does not achieve adequate luminal concentration and is reserved for ileus with inability to tolerate oral therapy, used alongside oral/rectal vancomycin.
• E. Oral metronidazole is no longer first-line due to inferior cure rates compared to vancomycin and fidaxomicin.

A rise in breath hydrogen of 20 ppm or more above baseline after lactose ingestion, accompanied by symptoms, is diagnostic of lactose malabsorption. Undigested lactose is fermented by colonic bacteria, producing hydrogen gas that is absorbed and exhaled. The temporal correlation between the hydrogen rise, symptom onset, and subsequent decline supports lactose intolerance rather than a nonspecific functional disorder. Small intestinal bacterial overgrowth would classically show an early rise in hydrogen within the first 60-90 minutes reflecting fermentation in the proximal small bowel, before the substrate reaches the colon, rather than a single later colonic peak.

• A. Celiac disease is not diagnosed by hydrogen breath testing; it requires serology and duodenal biopsy.
• B. The rise of 24 ppm above baseline with concurrent symptoms is a positive result, not negative; IBS is a diagnosis of exclusion and this test specifically points to lactose malabsorption.
• C. SIBO typically shows an early double peak or rise within the first 90 minutes reflecting small bowel fermentation, not a single late colonic-pattern rise.
• E. The 24 ppm rise exceeds the standard 20 ppm threshold for a positive test; this is a clear positive, not an indeterminate result.

This patient meets criteria for antiviral treatment of chronic hepatitis B: HBeAg-positive disease with persistently elevated ALT (more than twice the upper limit of normal) and HBV DNA greater than 20,000 IU/mL, indicating active immune-active chronic hepatitis. Tenofovir (disoproxil fumarate or alafenamide) is a preferred first-line agent due to its high potency, favorable resistance profile, and once-daily oral dosing. Entecavir is an equally acceptable first-line alternative. Treatment aims to suppress viral replication, reduce hepatic inflammation, and prevent progression to cirrhosis and hepatocellular carcinoma.

• B. Interferon is an option in selected patients but is not preferred first-line due to its side effect profile and the need for subcutaneous injection; oral nucleos(t)ide analogues are generally preferred.
• C. Lamivudine has a low barrier to resistance and high rates of viral breakthrough; it is no longer recommended as first-line therapy.
• D. This patient has active disease meeting treatment criteria (elevated ALT, high HBV DNA, HBeAg positive); observation alone would allow ongoing liver injury and risk of progression.
• E. Liver transplantation is not indicated; this patient does not have decompensated cirrhosis or end-stage liver disease.

Canadian guidelines recommend one-time hepatitis C antibody screening for all adults born between 1945 and 1975, reflecting the birth cohort effect where this group has a substantially higher prevalence of undiagnosed chronic hepatitis C due to historical transmission patterns before blood supply screening and harm reduction measures were widespread. This patient, born in 1968, falls within that cohort regardless of reported risk factors, since many patients with chronic hepatitis C are unaware of past exposures or remain asymptomatic for decades. Identifying infection enables access to highly effective direct-acting antiviral therapy, which cures over 95% of cases and prevents progression to cirrhosis and hepatocellular carcinoma.

• A. Hepatitis B screening is a separate consideration based on different risk criteria and does not substitute for birth-cohort hepatitis C screening.
• B. Birth cohort alone, independent of identifiable risk factors, is sufficient indication for one-time screening given the disproportionately high undiagnosed prevalence in this group.
• D. Antibody testing is the appropriate initial screening test; RNA testing is reserved for confirming active infection after a positive antibody result.
• E. Repeated annual screening is not recommended for average-risk individuals; a one-time test is sufficient unless new risk factors arise.

This presentation, a middle-aged woman with pruritus, a predominantly cholestatic liver enzyme pattern (markedly elevated alkaline phosphatase with only mildly elevated transaminases), and elevated IgM, is classic for primary biliary cholangitis. Anti-mitochondrial antibody is positive in over 90-95% of patients with primary biliary cholangitis and is highly specific, making it the key diagnostic marker alongside the cholestatic biochemical pattern. Autoimmune hepatitis, in contrast, typically presents with a hepatocellular pattern of injury (ALT and AST markedly elevated), elevated IgG, and antibodies such as anti-smooth muscle antibody, anti-liver kidney microsomal antibody, or anti-nuclear antibody.

• B. Anti-smooth muscle antibody is associated with autoimmune hepatitis, which presents with a hepatocellular rather than cholestatic enzyme pattern and elevated IgG rather than IgM.
• C. Anti-nuclear antibody with elevated IgG is characteristic of autoimmune hepatitis, which shows a hepatocellular rather than cholestatic biochemical pattern.
• D. Anti-liver kidney microsomal antibody type 1 is associated with type 2 autoimmune hepatitis, typically seen with hepatocellular injury, not this cholestatic presentation.
• E. Double-stranded DNA antibody is associated with systemic lupus erythematosus, not the specific liver disease suggested by this cholestatic pattern.

An ascitic fluid absolute neutrophil (polymorphonuclear leukocyte) count greater than 250 cells/mm³ is the diagnostic criterion for spontaneous bacterial peritonitis, regardless of whether ascitic fluid culture is positive, since culture is negative in up to 40% of true cases. Empiric antibiotic therapy, typically with intravenous cefotaxime or ceftriaxone, should be started as soon as this threshold is met without waiting for culture results. The serum-ascites albumin gradient helps determine the cause of ascites (portal hypertensive versus other), but does not diagnose infection, and features like elevated protein, low glucose, or high LDH are more suggestive of secondary bacterial peritonitis from a perforation or abscess rather than spontaneous infection.

• A. Ascitic LDH exceeding serum LDH, along with low glucose and very high protein, suggests secondary bacterial peritonitis from a surgical source, not spontaneous bacterial peritonitis.
• B. Elevated ascitic protein alone is nonspecific and does not establish infection; it is more useful in distinguishing transudate from exudate or raising suspicion for secondary peritonitis.
• C. A markedly low ascitic glucose is more characteristic of secondary peritonitis or malignancy than spontaneous bacterial peritonitis.
• E. A high serum-ascites albumin gradient indicates portal hypertension as the cause of ascites, not infection.

Patients with cirrhosis, regardless of the underlying etiology, are at increased risk of hepatocellular carcinoma (HCC) and should undergo surveillance with abdominal ultrasound combined with serum alpha-fetoprotein (AFP) every 6 months. This combination improves detection sensitivity for early-stage HCC compared with either test alone, allowing for curative treatment options. CT and MRI are reserved for further characterization of suspicious lesions identified on ultrasound, not as first-line surveillance tools due to cost and radiation or contrast exposure.

• B. Routine liver biopsy is not part of HCC surveillance protocols.
• C. MRI is reserved for characterizing indeterminate nodules found on ultrasound, not routine surveillance.
• D. CT is not first-line surveillance due to cost, radiation, and contrast exposure; it is used for lesion characterization.
• E. AFP alone has lower sensitivity than combined ultrasound and AFP and should not be used in isolation.

Non-alcoholic fatty liver disease (NAFLD) is strongly associated with obesity, type 2 diabetes, and metabolic syndrome, and is now the most common cause of chronic liver disease. Diagnosis requires imaging or histologic evidence of hepatic steatosis plus exclusion of significant alcohol consumption and other causes of fatty liver or elevated transaminases, such as viral hepatitis, hemochromatosis, Wilson disease, and autoimmune hepatitis, all of which have been excluded here. This patient's minimal alcohol intake does not meet the threshold for alcohol-related liver disease.

• B. Her alcohol intake is well below the threshold required to diagnose alcohol-related liver disease.
• C. Normal ferritin makes hemochromatosis unlikely.
• D. Normal ceruloplasmin and her age make Wilson disease unlikely.
• E. Autoimmune antibodies are negative, making this diagnosis unlikely.

Abdominal ultrasound is the first-line imaging test for suspected acute cholecystitis because it is widely available, inexpensive, fast, and has good sensitivity for detecting gallstones, gallbladder wall thickening (greater than 3 mm), pericholecystic fluid, and a sonographic Murphy sign. If the diagnosis remains unclear after ultrasound, a HIDA scan can be used as it has higher sensitivity and specificity but is more time-consuming and less available. Early laparoscopic cholecystectomy, ideally within 72 hours of symptom onset, is the definitive management once the diagnosis is confirmed.

• B. MRCP is used to evaluate the bile ducts for choledocholithiasis, not as first-line for cholecystitis.
• C. ERCP is a therapeutic procedure for bile duct stones, not a diagnostic test for cholecystitis.
• D. CT is less sensitive than ultrasound for gallbladder pathology and involves radiation exposure.
• E. HIDA scan is reserved for cases where ultrasound findings are equivocal, not as the initial test.

This patient has Reynolds pentad (fever, jaundice, right upper quadrant pain, hypotension, and confusion), indicating severe acute cholangitis with biliary sepsis, most commonly due to choledocholithiasis obstructing the common bile duct. After initial resuscitation with intravenous fluids and antibiotics, urgent biliary decompression with ERCP is required to relieve the obstruction and drain infected bile, as delay increases the risk of septic shock and death. Cholecystectomy addresses the gallbladder but does not relieve ductal obstruction and is not the urgent priority.

• A. Outpatient referral is inappropriate given this patient's severe sepsis requiring emergency intervention.
• C. Cholecystostomy drains the gallbladder, not the obstructed common bile duct, and is reserved for patients unfit for ERCP.
• D. Cholecystectomy does not address the common bile duct obstruction and is not urgent in this septic patient.
• E. Ursodeoxycholic acid is used for gallstone dissolution in select cases, not for acute cholangitis.

The revised Atlanta classification requires two of three criteria for diagnosing acute pancreatitis: characteristic abdominal pain, serum lipase or amylase elevated to at least three times the upper limit of normal, and characteristic findings on imaging. This patient's epigastric pain radiating to the back plus lipase elevation above three times normal already satisfies two criteria, confirming the diagnosis regardless of ultrasound findings, which can be normal early in the disease course. Imaging is not required to make the diagnosis when clinical and biochemical criteria are already met and is typically reserved for diagnostic uncertainty or assessing complications.

• A. Lipase in this case is nearly double, not below, the threshold; combined with typical pain it still meets two of three Atlanta criteria for diagnosis.
• C. Imaging can be normal in early acute pancreatitis and is not required when clinical and biochemical criteria are already met.
• D. Amylase is not required when lipase and clinical findings already satisfy two of the three diagnostic criteria.
• E. CT is not required for diagnosis when clinical and laboratory criteria are already satisfied; it is reserved for uncertain cases or complications.

This patient has several markers predicting severe acute pancreatitis, including tachycardia, tachypnea, hemoconcentration, and a rising blood urea nitrogen, which are associated with third-spacing and systemic inflammatory response. Current guidelines recommend early, goal-directed isotonic crystalloid resuscitation (such as lactated Ringer's solution) with frequent reassessment of hemodynamic status, urine output, and hematocrit to guide ongoing fluid therapy and avoid both under-resuscitation and fluid overload. Aggressive but monitored resuscitation reduces the risk of pancreatic necrosis and organ failure compared with fixed or restrictive strategies.

• B. A single bolus followed by oral intake alone does not provide adequate ongoing resuscitation in a patient with evolving severe pancreatitis.
• C. Fixed-rate fluids without reassessment risk under- or over-resuscitation in a dynamically changing clinical picture.
• D. Delaying fluids in a patient with signs of hypovolemia increases the risk of hypoperfusion and pancreatic necrosis.
• E. Fluid restriction is inappropriate in a patient with signs of hypovolemia and hemoconcentration from third-spacing.

Pancreatic enzyme replacement therapy (PERT) works by mixing with chyme in the duodenum, so enteric-coated capsules must be taken with or immediately before meals and snacks, divided throughout the day rather than as one large dose. Crushing enteric-coated preparations destroys the coating that protects lipase from gastric acid inactivation, reducing efficacy. Dosing is based on lipase units per meal and titrated against steatorrhea symptoms and weight gain. Proper timing with food intake is the single most important factor determining therapeutic response.

• A. Delayed dosing misses the window when enzymes need to mix with chyme in the duodenum.
• C. A single large dose does not cover enzyme needs for meals eaten later in the day.
• D. Crushing destroys the enteric coating, exposing lipase to gastric acid and inactivating it.
• E. Bedtime dosing away from meals means the enzymes are not present when food enters the duodenum.

Painless jaundice with a palpable gallbladder (Courvoisier sign) and a cholestatic liver panel in an older adult raises strong suspicion for pancreatic head adenocarcinoma causing biliary obstruction. Abdominal ultrasound is the recommended first-line, non-invasive, low-cost test to confirm biliary dilation and often identifies the level of obstruction or a pancreatic mass. Further cross-sectional imaging, such as CT or MRCP, is used subsequently for staging and surgical planning once ultrasound establishes obstructive jaundice. ERCP is reserved for cases requiring tissue sampling or therapeutic biliary stenting, not as an initial diagnostic step.

• B. ERCP is invasive and carries risks such as pancreatitis; it is used after initial imaging confirms obstruction or when therapy is needed.
• C. Liver biopsy does not establish the cause of biliary obstruction and carries unnecessary risk at this stage.
• D. CA 19-9 lacks sensitivity and specificity for diagnosis and is used for monitoring, not as a first test.
• E. MRCP gives more detail than ultrasound but is more costly and less readily available as a first-line test.

FENa is calculated as (urine Na × serum creatinine) / (serum Na × urine creatinine) × 100, giving (8 × 210) / (138 × 6000) × 100 ≈ 0.3%. A FENa below 1% indicates intact tubular sodium reabsorption, consistent with prerenal azotemia from volume depletion, which fits this patient's vomiting, tachycardia, and hypotension. A bland urinalysis without casts or protein further supports a prerenal cause rather than intrinsic renal damage. In acute tubular necrosis, tubular injury impairs sodium reabsorption, producing a FENa typically above 2% along with granular casts on urinalysis.

• A. The FENa value of 0.3% is correct but ATN is incorrect given the clinical picture and bland sediment.
• B. FENa is 0.3%, and prerenal azotemia is actually the correct category, but the stated FENa value is wrong.
• C. Postrenal obstruction would show hydronephrosis on imaging, not a low FENa, and no obstructive symptoms are described.
• D. The calculated FENa is 0.3%, not 2.5%, and the bland urinalysis argues against ATN.

Volume expansion with isotonic intravenous saline before and after contrast administration is the best-supported measure for preventing contrast-induced nephropathy in patients with reduced kidney function, improving renal perfusion and promoting contrast clearance. Trials have not shown N-acetylcysteine to provide consistent benefit, and sodium bicarbonate has not demonstrated clear superiority over saline. Diuretics such as furosemide can cause volume depletion and worsen renal perfusion, so they are avoided. Prophylactic dialysis has no proven role in prevention and is not indicated for this purpose.

• A. A single bicarbonate bolus without a hydration protocol is not established as effective prophylaxis.
• B. Dialysis does not prevent contrast nephropathy and is reserved for established renal failure requiring renal replacement.
• C. N-acetylcysteine has not shown consistent benefit in randomized trials and is not recommended as sole prophylaxis.
• E. Furosemide can cause volume depletion, worsening renal perfusion and increasing the risk of contrast-induced nephropathy.

The combination of a temporal relationship to a new drug (a fluoroquinolone, a well-recognized cause), fever, rash, and urine eosinophils with white cell casts is classic for acute interstitial nephritis, a hypersensitivity reaction within the renal interstitium. Acute tubular necrosis typically follows ischemic or nephrotoxic insults and shows granular or muddy brown casts rather than white cell casts or eosinophiluria. The systemic allergic features (fever, rash, eosinophiluria) distinguish AIN from an infectious or ischemic process. Withdrawal of the offending drug is the key management step.

• A. RPGN presents with red cell casts and significant proteinuria/hematuria from glomerular injury, not eosinophiluria.
• B. No signs of localized infection, flank pain, or abscess on imaging are described, and the systemic allergic picture is not typical of pyelonephritis.
• C. Minimal change disease causes nephrotic-range proteinuria, not this presentation with fever, rash, and casts.
• D. ATN shows granular or muddy brown casts on urinalysis, not white cell casts or eosinophiluria, and lacks the allergic features described.

This patient has hyperphosphatemia with secondary hyperparathyroidism from CKD-mineral bone disease, and a non-calcium-based phosphate binder such as sevelamer is preferred because her serum calcium is already at the upper end of normal, and calcium-based binders risk vascular calcification and hypercalcemia with chronic use. Sevelamer binds dietary phosphate in the gut, reducing absorption without contributing to calcium load. Calcitriol would be considered to directly suppress PTH once phosphate is controlled, but giving it with elevated phosphate risks worsening calcium-phosphate product and metastatic calcification. Cinacalcet lowers PTH via the calcium-sensing receptor but does not address the phosphate elevation directly and is typically used in dialysis-dependent CKD.

• A. Calcium carbonate would add to calcium load in a patient whose calcium is already at the upper limit, risking hypercalcemia and vascular calcification.
• B. Calcitriol can worsen hyperphosphatemia and calcium-phosphate product if given before phosphate is controlled.
• C. Furosemide does not correct phosphate retention and is not indicated for mineral bone disease management.
• E. Cinacalcet targets PTH directly via the calcium-sensing receptor and is not first-line for phosphate control, nor typically used pre-dialysis.

This patient demonstrates multiple classic emergent indications for dialysis, summarized by the mnemonic AEIOU: refractory acidosis, electrolyte imbalance (severe hyperkalemia unresponsive to medical therapy), and fluid overload causing pulmonary edema unresponsive to diuretics, in the setting of advanced CKD. When hyperkalemia with ECG changes persists despite calcium, insulin-dextrose, and beta-agonist therapy, and pulmonary edema does not respond to loop diuretics, emergent hemodialysis is required to directly remove potassium and excess fluid. Medical therapies are temporizing measures and do not substitute for dialysis when refractory. Delaying dialysis in this scenario risks fatal arrhythmia or respiratory failure.

• A. Diuretics have already failed to resolve the pulmonary edema, indicating a need for dialysis rather than escalating a failed therapy.
• B. Bicarbonate has limited effect in a patient already treated with multiple shifting therapies and does not address refractory fluid overload.
• C. Kayexalate acts too slowly to address this acute, life-threatening hyperkalemia with ECG changes and pulmonary edema.
• D. Calcium gluconate only stabilizes the cardiac membrane transiently and does not remove potassium or correct the underlying overload and acidosis.

ACE inhibitors and ARBs reduce angiotensin II-mediated vasoconstriction, which acts predominantly on the efferent arteriole. This lowers intraglomerular capillary pressure, reducing hyperfiltration and proteinuria independent of systemic blood pressure effects. A small rise in creatinine (up to 30%) and mild increase in potassium are expected and acceptable, reflecting the intended hemodynamic effect rather than toxicity. This renoprotective effect is the basis for ACE inhibitor/ARB use as first-line therapy in diabetic kidney disease with albuminuria. Creatinine and potassium should be monitored within 1-2 weeks of initiation or dose change.

• A. This describes SGLT2 inhibitors, a different drug class with a distinct renoprotective mechanism.
• C. Afferent dilation would increase, not decrease, intraglomerular pressure, worsening proteinuria.
• D. The antiproteinuric effect is substantially mediated by direct glomerular hemodynamic changes, not blood pressure alone.
• E. Aldosterone suppression contributes a minor effect but is not the primary mechanism of proteinuria reduction.

Minimal change disease is the most common cause of nephrotic syndrome in children, typically presenting with sudden edema, severe hypoalbuminemia, and normal renal function, and it is usually steroid-responsive without biopsy in typical childhood cases. Membranous nephropathy is a common cause of nephrotic syndrome in adults and is associated with secondary causes such as hepatitis B infection, with biopsy showing subepithelial immune deposits and basement membrane thickening ("spike and dome" appearance). The combination of age, clinical course, and biopsy findings distinguishes these two entities. Recognizing age-typical patterns guides whether empiric steroid therapy or biopsy is the appropriate next step.

• A. FSGS typically shows segmental sclerosis on biopsy, not the diffuse basement membrane thickening with subepithelial deposits described in the man.
• C. Membranoproliferative GN shows mesangial and endothelial proliferation, not the sudden edematous presentation with normal renal function in the child.
• D. FSGS and IgA nephropathy do not match the clinical and biopsy findings described, and IgA nephropathy is nephritic, not purely nephrotic.
• E. Membranous nephropathy is uncommon in young children and minimal change disease does not show subepithelial deposits on biopsy.

IgA nephropathy classically presents with episodic gross hematuria occurring synchronously or within 1-2 days of an upper respiratory or mucosal infection ("synpharyngitic hematuria"), with normal complement levels. The short latency distinguishes it from post-streptococcal glomerulonephritis, which typically occurs 1-3 weeks after infection and is associated with low complement C3. Dysmorphic red blood cells and red cell casts confirm a glomerular source of bleeding, defining a nephritic pattern. Diagnosis is confirmed by renal biopsy showing mesangial IgA deposits, though this is often deferred in mild, self-limited presentations.

• A. Lupus nephritis occurs with other systemic features of SLE and typically with low complement levels, not isolated post-infectious hematuria.
• B. MPGN typically presents with a more chronic nephrotic-nephritic picture and often with low complement, not an acute synpharyngitic episode.
• D. Post-streptococcal GN has a longer latency of 1-3 weeks after infection and is associated with low serum complement.
• E. Anti-GBM disease typically causes rapidly progressive renal failure with pulmonary hemorrhage (Goodpasture syndrome), not a mild self-limited episode.

The first step in hyponatremia workup is confirming it is hypotonic (true) hyponatremia by measuring serum osmolality, which is low here at 255 mOsm/kg, excluding pseudohyponatremia from hyperglycemia or hyperlipidemia. The next step in a patient who appears clinically euvolemic is to measure urine osmolality and urine sodium to assess whether the kidney is appropriately diluting urine and to help distinguish SIADH from other euvolemic causes. Urine osmolality that is inappropriately concentrated relative to the low serum osmolality suggests impaired water excretion, as in SIADH. This stepwise approach (osmolality, then volume status, then urine studies) is the standard algorithm for hyponatremia evaluation.

• A. Proteinuria assessment is relevant to nephrotic syndrome causing hypervolemic hyponatremia, which is excluded here by the absence of edema.
• B. Cortisol is checked after urine studies to exclude adrenal insufficiency as a cause of euvolemic hyponatremia, not as the immediate next test.
• D. Triglycerides would be relevant if pseudohyponatremia from hyperlipidemia were suspected, but the measured low osmolality already confirms true hyponatremia.
• E. TSH is a secondary investigation for hypothyroidism-associated hyponatremia, not the immediate next step after confirming hypotonicity.

This patient meets diagnostic criteria for SIADH: hypotonic hyponatremia, euvolemia, inappropriately concentrated urine (osmolality greater than serum osmolality and above 100 mOsm/kg), urine sodium above 30 mmol/L, and normal thyroid, adrenal, and renal function with no diuretic use, in the setting of a known cause (small cell lung cancer, an ectopic ADH source). First-line management of chronic, mild to moderate, asymptomatic SIADH is fluid restriction to below 1 litre per day to create a negative free water balance. Hypertonic saline and vasopressin receptor antagonists are reserved for severe, symptomatic, or refractory cases. Isotonic saline is ineffective and can worsen hyponatremia in SIADH because the concentrated urine excretes the sodium and retains free water.

• A. Hypertonic saline is reserved for severe or symptomatic hyponatremia (e.g., seizures, severe confusion), not asymptomatic chronic hyponatremia.
• B. Normal saline is ineffective in SIADH because the urine is more concentrated than the infused fluid, leading to net free water retention and worsening hyponatremia.
• C. Desmopressin would worsen SIADH by further promoting water retention and is used instead to prevent overly rapid correction in other hyponatremia contexts.
• E. Tolvaptan is reserved for cases refractory to fluid restriction or when fluid restriction is not feasible, not first-line therapy.

This patient has severe hyperkalemia with ECG changes indicating cardiac membrane instability (absent P waves, widened QRS), placing him at imminent risk of ventricular arrhythmia or asystole. Intravenous calcium gluconate is given first because it stabilizes the cardiac cell membrane within minutes by antagonizing the effect of hyperkalemia on myocardial conduction, although it does not lower serum potassium. Insulin with dextrose and salbutamol are given next to shift potassium intracellularly, followed by removal of potassium from the body via dialysis, since this patient's definitive treatment is urgent hemodialysis. Sodium polystyrene sulfonate and bicarbonate have a slower onset and are not appropriate as the immediate first step in a patient with ECG changes.

• A. Bicarbonate has a limited and delayed effect on potassium shift and is not first-line in acute severe hyperkalemia with ECG changes.
• B. Insulin-glucose shifts potassium intracellularly but has no effect on cardiac membrane stability, so it should follow calcium when ECG changes are present.
• C. Salbutamol also shifts potassium intracellularly but acts more slowly than calcium and does not address membrane instability.
• D. Oral potassium binders act over hours and are too slow for a patient with ECG changes requiring immediate stabilization.

For recurrent calcium oxalate stone formers, the cornerstone of dietary prevention is increasing fluid intake to achieve a urine output of at least 2 to 2.5 litres per day, which dilutes stone-forming solutes. Dietary calcium should not be restricted, because low calcium intake increases intestinal oxalate absorption and paradoxically raises stone risk; normal dietary calcium (around 1000 to 1200 mg per day) is recommended instead. Sodium and animal protein intake should be limited, and oxalate-rich foods moderated, while citrate intake (from fruits) can be encouraged to counteract his low urinary citrate. High-dose vitamin C supplementation increases oxalate excretion and should be avoided in oxalate stone formers.

• A. High animal protein intake increases urinary calcium and uric acid excretion while lowering citrate, worsening stone risk rather than helping.
• B. Restricting dietary calcium increases oxalate absorption and worsens oxalate stone risk; normal calcium intake is recommended instead.
• C. High-dose vitamin C is metabolized to oxalate and increases urinary oxalate excretion, worsening calcium oxalate stone risk.
• E. Restricting fluid intake concentrates urine and increases supersaturation of stone-forming salts, increasing stone risk.

Non-contrast CT of the abdomen and pelvis is the most sensitive and specific imaging study for suspected renal colic, detecting stones of nearly all compositions and sizes while also identifying alternative diagnoses such as appendicitis or aortic pathology. Ultrasound is preferred in pregnant patients and children to avoid radiation but has lower sensitivity, particularly for ureteral stones. This patient has no contraindication to CT and benefits from its superior diagnostic accuracy for a first presentation of suspected nephrolithiasis.

• A. Plain radiography misses radiolucent stones and has poor sensitivity overall.
• B. MR urography is costly, less available, and not superior to CT for stone detection; it is not first-line.
• C. Ultrasound has lower sensitivity for ureteral stones and is reserved for pregnant patients or children to limit radiation exposure.
• D. Intravenous pyelogram has been largely replaced by CT due to lower sensitivity and the need for contrast.

The Hypertension Canada algorithm requires out-of-office confirmation (ambulatory blood pressure monitoring, ABPM, or home blood pressure monitoring, HBPM) for most patients with an elevated AOBP before diagnosing hypertension, since office readings alone can misclassify patients due to white-coat effect. Exceptions allowing office-only diagnosis include AOBP at or above 180/110 mmHg or presence of macrovascular target organ damage, neither of which applies here. Confirming out of office avoids unnecessary lifelong pharmacotherapy in patients with white-coat hypertension.

• A. A single AOBP reading, without out-of-office confirmation or severe elevation, is insufficient for diagnosis per the algorithm.
• B. Starting treatment without out-of-office confirmation risks overdiagnosis and unnecessary medication in a patient who may have white-coat hypertension.
• D. Waiting a full year without further workup delays diagnosis in a patient with a clearly elevated reading.
• E. Secondary hypertension workup is not indicated before confirming the diagnosis of hypertension itself.

In patients with diabetes and hypertension, Hypertension Canada recommends an ACE inhibitor or angiotensin receptor blocker as first-line therapy, particularly given their renoprotective effects and reduction in cardiovascular events in this population. Thiazide diuretics, long-acting calcium channel blockers, or ACE inhibitors/ARBs are all acceptable first-line options in diabetes, but ACE inhibitors or ARBs are preferred when there are additional cardiovascular risk factors or any degree of kidney involvement. Beta-blockers are not first-line for uncomplicated hypertension unless another compelling indication exists, and alpha-blockers are not recommended as first-line monotherapy.

• A. Calcium channel blockers are an acceptable alternative but ACE inhibitors are preferred in diabetes for their renoprotective benefit.
• C. Alpha-blockers are not recommended as first-line monotherapy for hypertension.
• D. Thiazide diuretics are acceptable but not preferred over ACE inhibitors/ARBs in diabetic patients with additional risk factors.
• E. Beta-blockers are not first-line for uncomplicated hypertension without a compelling indication such as coronary artery disease.

Fibromuscular dysplasia is the most common cause of renovascular hypertension in young women, typically presenting with resistant hypertension, an abdominal bruit, and mild hypokalemia from secondary hyperaldosteronism driven by renal hypoperfusion. Atherosclerotic renal artery stenosis typically occurs in older patients with vascular risk factors such as smoking, diabetes, or established atherosclerosis, which this patient lacks. The clinical picture of a young, otherwise healthy woman with resistant hypertension and an abdominal bruit is classic for fibromuscular dysplasia rather than a primary adrenal or aortic process.

• A. Pheochromocytoma presents with episodic headache, palpitations, and diaphoresis rather than a continuous abdominal bruit.
• B. Primary hyperaldosteronism does not produce an abdominal bruit and typically shows more pronounced hypokalemia without a vascular cause.
• C. Atherosclerotic disease typically occurs in older patients with vascular risk factors, which this patient does not have.
• D. Coarctation of the aorta typically presents with differential blood pressures between upper and lower extremities and is usually diagnosed earlier in life.

This patient has a hypertensive emergency with evidence of end-organ damage (hypertensive retinopathy with hemorrhages and papilledema), requiring controlled intravenous antihypertensive therapy. The recommended target is to reduce mean arterial pressure by no more than 25% within the first hour to avoid precipitating cerebral, cardiac, or renal hypoperfusion from overly rapid correction. Sublingual or rapid-acting oral agents like immediate-release nifedipine are contraindicated due to the risk of precipitous, uncontrolled blood pressure drops. Normalization of blood pressure should occur gradually over subsequent hours to days, not within the first hour.

• A. This patient has end-organ damage and requires urgent treatment, not discharge.
• B. Observation alone is inappropriate given evidence of hypertensive emergency with target organ damage.
• C. Rapid-acting oral nifedipine causes uncontrolled, unpredictable drops in blood pressure and is contraindicated in hypertensive emergency.
• E. Normalizing blood pressure within one hour risks organ hypoperfusion from overly rapid correction.

Diabetes Canada criteria require a confirmatory test on a separate day for diagnosis in an asymptomatic individual, using fasting plasma glucose (≥7.0 mmol/L), A1C (≥6.5%), or a 2-hour oral glucose tolerance test value (≥11.1 mmol/L), unless there is unequivocal hyperglycemia with classic symptoms of hyperglycemia or a hyperglycemic crisis. This patient's single fasting value of 7.3 mmol/L meets the diagnostic threshold but requires confirmation with a repeat fasting glucose or A1C on another day because he is asymptomatic. A random glucose or urine dipstick is not sufficiently specific for diagnosis.

• A. An oral glucose tolerance test is an alternative diagnostic test, not conditional on the fasting glucose being below threshold.
• B. Urine glucose testing is not a validated diagnostic criterion for diabetes.
• D. A random plasma glucose test does not meet the standardized diagnostic criteria and is not used for confirmation in an asymptomatic patient.
• E. A single abnormal fasting glucose in an asymptomatic patient requires confirmatory testing before diagnosis per Diabetes Canada guidelines.

Metformin is renally cleared and not metabolized, so impaired kidney function leads to drug accumulation and increases the risk of lactic acidosis, a rare but serious adverse effect related to inhibition of hepatic gluconeogenesis and mitochondrial effects on lactate metabolism. At an eGFR between 30 and 45 mL/min/1.73m², Diabetes Canada recommends dose reduction and increased monitoring rather than an absolute contraindication, while metformin is generally avoided below an eGFR of 30 mL/min/1.73m². Metformin does not cause hypoglycemia as monotherapy since it works by decreasing hepatic glucose production rather than stimulating insulin secretion.

• A. Metformin does not cause hypoglycemia as monotherapy because it does not stimulate insulin secretion.
• C. Metformin is weight-neutral or associated with modest weight loss, not weight gain.
• D. Euglycemic DKA is a known risk of SGLT2 inhibitors, not metformin.
• E. Metformin is not associated with pancreatitis; this is a concern with other drug classes such as GLP-1 receptor agonists.

SGLT2 inhibitors can precipitate euglycemic diabetic ketoacidosis, characterized by a high anion gap metabolic acidosis with ketosis despite only mildly elevated or near-normal blood glucose, because glucosuria lowers plasma glucose while insulin deficiency and increased glucagon promote ketogenesis. This risk is increased with volume depletion, acute illness, reduced carbohydrate intake, or perioperative states, and SGLT2 inhibitors should be held during acute illness or before surgery. Hyperosmolar hyperglycemic state requires markedly elevated glucose, which is not seen here, and the ketotic picture with only modest hyperglycemia is the key distinguishing feature.

• B. There is no history of contrast exposure, and this presentation is explained by ketoacidosis, not nephropathy.
• C. There is no abdominal pain or lipase elevation described to suggest pancreatitis.
• D. Lactic acidosis presents with an elevated lactate rather than significant ketosis, and is not a typical SGLT2 inhibitor effect.
• E. Hyperosmolar hyperglycemic state requires severe hyperglycemia, typically above 33 mmol/L, which is absent here.

The first step in DKA management is volume resuscitation with isotonic (0.9%) saline to restore intravascular volume and renal perfusion, which also helps lower glucose and counter-regulatory hormones. Insulin should not be started until volume repletion is underway and only after confirming potassium is not low, because insulin drives potassium intracellularly and can precipitate dangerous hypokalemia. This patient's potassium is elevated (5.8 mmol/L), likely due to acidosis and insulin deficiency, so potassium replacement is not yet needed but insulin can proceed safely once fluids have started. Bicarbonate is reserved for severe refractory acidosis (pH less than 6.9) and is not routinely used.

• A. Bicarbonate is not indicated here; it is reserved for extreme acidosis (pH <6.9) and can cause paradoxical CNS acidosis and hypokalemia.
• B. Insulin should follow initiation of fluid resuscitation, not precede it, to avoid worsening hypotension and shifting potassium before volume is restored.
• D. Potassium is currently elevated (5.8 mmol/L), so replacement is not indicated at this stage; it will likely be needed once insulin lowers it.
• E. Dextrose is added once glucose falls to around 14 mmol/L to prevent hypoglycemia while continuing insulin, not as an initial step.

Hyperosmolar hyperglycemic state (HHS) is characterized by extreme hyperglycemia (often >33 mmol/L), very high serum osmolality (>320 mOsm/kg), minimal or absent ketosis, and near-normal pH/bicarbonate, typically in older patients with type 2 diabetes and preserved residual insulin secretion. In contrast, DKA presents with significant ketosis, a high anion gap metabolic acidosis, and glucose that is often less extreme. This patient's near-normal pH, absent ketones, and markedly elevated osmolality with severe hyperglycemia fit HHS rather than DKA. Management of HHS emphasizes aggressive fluid resuscitation, with insulin used more cautiously since acidosis is minimal.

• A. This combination (severe acidosis plus low osmolality) is inconsistent with this patient's near-normal pH and markedly elevated osmolality.
• B. Mild hyperglycemia with respiratory alkalosis does not match this patient's glucose of 44 mmol/L or his metabolic findings.
• C. Normal glucose with ketosis does not match this patient's severe hyperglycemia and is not characteristic of either DKA or HHS.
• E. This profile describes DKA, which this patient does not have given his normal pH and absent ketones.

Diabetes Canada's preferred approach to gestational diabetes screening is a two-step process: a 50 g glucose challenge test at 24-28 weeks' gestation, with a 75 g oral glucose tolerance test performed only if the initial screen is abnormal (1-hour glucose 7.8-11.0 mmol/L indicates need for further testing, and a value of 11.1 mmol/L or higher is diagnostic without further testing). The alternative, one-step approach uses a 75 g OGTT directly in all women but is used less commonly in Canada. HbA1c and random glucose are not validated screening tools for gestational diabetes. Fasting glucose alone lacks sufficient sensitivity for the two-step protocol.

• A. HbA1c is not recommended for gestational diabetes screening because pregnancy alters red cell turnover and glucose dynamics.
• B. Random plasma glucose is not a validated screening test for gestational diabetes.
• C. Fasting glucose alone is not an accepted stand-alone gestational diabetes screening method.
• D. This describes the alternative one-step approach, which is not the preferred protocol in Diabetes Canada guidelines.

An elevated TSH with a low free T4 confirms primary (overt) hypothyroidism, reflecting thyroid gland failure with loss of negative feedback inhibition of TSH. The standard starting dose of levothyroxine in otherwise healthy, non-elderly adults is approximately 1.6 micrograms/kg/day, with dose titration based on repeat TSH measurement after 6-8 weeks. Secondary hypothyroidism would show a low or inappropriately normal TSH with low free T4, and would require monitoring of free T4 rather than TSH because the pituitary-thyroid feedback loop is disrupted. Subclinical hypothyroidism refers to an elevated TSH with a normal free T4, which does not match this patient's low free T4.

• A. A fixed dose regardless of weight does not reflect weight-based dosing principles used for initiating levothyroxine.
• C. Her TSH is elevated, not low or normal, which rules out secondary (pituitary) hypothyroidism.
• D. Subclinical hypothyroidism requires a normal free T4; this patient's free T4 is low, indicating overt disease requiring treatment.
• E. The markedly abnormal TSH and free T4 already confirm primary hypothyroidism; treatment should not be delayed.

Methimazole is the preferred first-line antithyroid drug for Graves disease in most non-pregnant adults because of its once-daily dosing and lower risk of hepatotoxicity compared with propylthiouracil. Radioactive iodine is avoided in women planning pregnancy in the near term because it requires a delay of at least 6 months before conception and can worsen Graves ophthalmopathy. Surgery is reserved for large goiters with compressive symptoms, suspected malignancy, or when antithyroid drugs and radioactive iodine are contraindicated or declined. Propylthiouracil is reserved for the first trimester of pregnancy or thyroid storm because of its hepatotoxicity risk, not as routine first-line thertherapy.

• A. Radioactive iodine requires a delay before conception and may worsen her existing ophthalmopathy, making it a poor choice here.
• C. Propylthiouracil is not first-line outside of the first trimester of pregnancy or thyroid storm due to hepatotoxicity risk.
• D. Surgery is reserved for specific indications such as compressive symptoms or suspected malignancy, not as routine first-line therapy.
• E. Beta-blockers control adrenergic symptoms but do not treat the underlying hyperthyroidism and are not used as monotherapy.

The initial investigation for any thyroid nodule is a serum TSH level to determine functional status. If TSH is low, a radionuclide scan should follow to identify a hyperfunctioning (autonomous) nodule, which has a very low risk of malignancy and does not require biopsy. If TSH is normal or elevated, thyroid ultrasound is the next step to characterize the nodule's sonographic features and determine whether fine-needle aspiration biopsy is warranted based on size and risk stratification. Serum thyroglobulin is not useful in the initial workup of a thyroid nodule because it lacks specificity for malignancy.

• B. A radionuclide scan is only indicated if TSH is found to be low, not as the first test.
• C. Biopsy should follow ultrasound risk stratification, and is not the immediate next step before TSH and ultrasound.
• D. Thyroglobulin is not useful for initial nodule evaluation and is mainly used for post-thyroidectomy surveillance in differentiated thyroid cancer.
• E. Ultrasound is performed after TSH, since a low TSH changes the diagnostic pathway toward a radionuclide scan instead.

Primary adrenal insufficiency (Addison disease) results from destruction of the adrenal cortex, leading to low cortisol and aldosterone with compensatory elevation of ACTH due to loss of negative feedback; this elevated ACTH also causes hyperpigmentation through stimulation of melanocortin receptors. The cosyntropin (synthetic ACTH) stimulation test confirms the diagnosis when cortisol fails to rise adequately (generally remaining below 500 nmol/L) because the adrenal gland cannot respond to ACTH stimulation. Electrolyte findings of hyponatremia and hyperkalemia reflect concurrent aldosterone deficiency causing renal sodium loss and potassium retention. Secondary adrenal insufficiency would show low ACTH with a blunted but sometimes partially preserved cortisol response, and typically without hyperkalemia or hyperpigmentation.

• A. Low ACTH with normal cortisol response is inconsistent with primary adrenal failure and does not fit the hyperpigmentation and electrolyte pattern.
• B. A normal cortisol rise after stimulation would argue against primary adrenal insufficiency, not confirm it.
• C. Low ACTH would suggest secondary, not primary, adrenal insufficiency, and would not explain her hyperpigmentation.
• E. A normal ACTH and normal cortisol response would exclude, not confirm, primary adrenal insufficiency.