SMLE nephrology questions

The combination of hypotonic hyponatremia (serum osmolality <275 mOsm/kg) with inappropriately concentrated urine (urine osmolality >100 mOsm/kg) and elevated urine sodium (>40 mmol/L) in a clinically euvolemic patient (no edema, no signs of dehydration, normal blood pressure) is diagnostic of SIADH. In hypovolemic hyponatremia from extrarenal losses, the kidney conserves sodium, so urine sodium is typically low (<20-30 mmol/L) unless a diuretic is causing renal sodium wasting. Normal thyroid and adrenal function excludes hypothyroidism and adrenal insufficiency as mimics. SIADH is diagnosed by exclusion of other causes of euvolemic hypotonic hyponatremia plus the biochemical criteria above.

• A. Primary polydipsia causes dilute urine (low urine osmolality), not concentrated urine as seen here.
• B. There is no diarrhea reported, and GI losses causing hypovolemic hyponatremia would produce a low urine sodium due to renal sodium avidity.
• D. No history of diuretic use is given, and diuretic use would still require euvolemic or mildly hypovolemic status with a plausible drug history.

This patient has severe, likely chronic hyponatremia (symptoms over months, no severe neurologic signs) and is at high risk of osmotic demyelination syndrome if corrected too rapidly. Current guidelines recommend limiting the correction rate to a maximum of 8 mmol/L in any 24-hour period (some use 6-8 mmol/L in high-risk patients, such as the elderly, alcoholics, or malnourished patients) and no more than 18 mmol/L over 48 hours. Overcorrection risks irreversible central pontine and extrapontine myelinolysis, presenting days later with quadriparesis, dysarthria, or altered consciousness. If overcorrection occurs, it can be managed with desmopressin and hypotonic fluids (relowering strategy).

• A. A rise of 15 mmol/L or more in 24 hours exceeds the recommended safe limit and increases demyelination risk.
• B. Full correction to normal sodium within 24 hours in chronic hyponatremia greatly exceeds the safe limit and risks osmotic demyelination.
• D. Sodium should be carefully monitored and corrected at a controlled rate, not left to normalize unpredictably, which risks both undercorrection and rebound overcorrection.

ECG changes of hyperkalemia (peaked T waves, widened QRS, loss of P waves) indicate a risk of imminent life-threatening arrhythmia, and intravenous calcium gluconate should be given immediately to stabilize the cardiac membrane. Calcium works within minutes by antagonizing the effect of hyperkalemia on cardiac myocyte excitability, but it does not lower serum potassium. Insulin-dextrose and dialysis are essential subsequent steps to actually lower serum potassium, but they act more slowly and should not delay membrane-stabilizing therapy. Sodium polystyrene sulfonate acts over hours and has no role in an acute emergency with ECG changes.

• A. Dialysis is definitive therapy but takes time to arrange; calcium gluconate must be given first to protect the myocardium.
• C. Insulin-dextrose lowers potassium but takes 15-30 minutes to act and does not provide immediate cardiac membrane stabilization.
• D. Sodium polystyrene sulfonate acts slowly over hours and is inappropriate for acute ECG changes requiring immediate stabilization.

Insulin activates the Na-K-ATPase pump on cell membranes, driving potassium into cells and transiently lowering serum potassium without changing total body potassium; dextrose is co-administered to prevent hypoglycemia. Sodium polystyrene sulfonate is a cation-exchange resin that works in the gastrointestinal tract, binding potassium in exchange for sodium and promoting potassium excretion in the stool, thereby lowering total body potassium, though it acts over hours. These two therapies are complementary: insulin provides rapid but temporary redistribution, while resins (or dialysis) provide actual potassium removal from the body. Beta-agonists such as nebulized salbutamol work by a similar intracellular shift mechanism as insulin, via beta-2 receptor-mediated Na-K-ATPase stimulation.

• A. This reverses the actual mechanisms of both drugs.
• B. This reverses the mechanisms: insulin causes an intracellular shift, it does not act on the kidney, and the resin does not shift potassium intracellularly.
• C. Insulin does not bind potassium directly, and the resin does not act on the kidney; both statements are incorrect.

The triad of hypertension, hypokalemia, and metabolic alkalosis with a high aldosterone-to-renin ratio (elevated aldosterone, suppressed renin) is classic for primary hyperaldosteronism, most commonly due to an aldosterone-producing adenoma or bilateral adrenal hyperplasia. Excess aldosterone increases distal tubular sodium reabsorption and potassium/hydrogen secretion, causing hypertension, hypokalemia, and alkalosis. Diuretic use is excluded here by history and would typically show a variable renin level depending on volume status, not a suppressed renin with elevated aldosterone. Confirmatory testing includes a saline infusion or oral sodium loading test, followed by adrenal CT and possibly adrenal vein sampling to localize the source.

• A. The patient denies diuretic use, and diuretics causing hypokalemic alkalosis would be associated with elevated renin due to volume contraction, not suppressed renin.
• B. Renal artery stenosis causes hypertension with elevated renin and secondary hyperaldosteronism, not a suppressed renin level.
• C. Bartter syndrome is a renal tubular disorder causing hypokalemic alkalosis with elevated renin and aldosterone but normal or low blood pressure, not hypertension.

The anion gap is calculated as Na − (Cl + HCO3) = 140 − (100 + 9) = 31 mmol/L, which is markedly elevated above the normal range of 8-12 mmol/L, confirming a high anion gap metabolic acidosis. The clinical context of ingestion of a methanol-containing product (windshield washer fluid) with altered mental status strongly suggests toxic alcohol poisoning, which produces a high anion gap and often an elevated osmolar gap due to unmeasured organic acids. Other causes of high anion gap acidosis include diabetic ketoacidosis, lactic acidosis, and uremia, but the history here points specifically to toxic alcohol ingestion. Management includes fomepizole, correction of acidosis, and consideration of hemodialysis for severe cases.

• A. The low pH confirms acidemia, not alkalemia, so this is not a primary respiratory alkalosis.
• B. The anion gap is clearly elevated (31 mmol/L), not normal, which excludes a hyperchloremic normal anion gap acidosis such as from diarrhea.
• D. While uremia can cause a high anion gap acidosis, the clinical history of toxic ingestion is the more specific and likely explanation here, and no renal failure history is given.

Type 1 (distal) renal tubular acidosis results from impaired hydrogen ion secretion by the distal tubule, causing an inability to acidify the urine; urine pH remains inappropriately high (>5.5) despite systemic metabolic acidosis. The resulting chronic acidosis promotes bone calcium release and hypercalciuria, which together with reduced citrate excretion leads to nephrocalcinosis and nephrolithiasis, as seen in this patient. Type 2 (proximal) RTA involves a defect in bicarbonate reabsorption and is often associated with Fanconi syndrome, featuring glucosuria, phosphaturia, and aminoaciduria, none of which are present here, and urine pH can become acidic once filtered bicarbonate falls below the reduced reabsorptive threshold. Type 4 RTA is caused by aldosterone deficiency or resistance and is associated with hyperkalemia, which is inconsistent with this patient's hypokalemia.

• A. Proximal RTA typically presents with features of Fanconi syndrome (glucosuria, aminoaciduria, phosphaturia), which are absent here, and nephrocalcinosis is uncommon.
• B. Fanconi syndrome specifically involves generalized proximal tubular dysfunction with glucosuria, phosphaturia, and aminoaciduria, none of which are present in this patient.
• D. Type 4 RTA is associated with hyperkalemia due to aldosterone deficiency or resistance, not the hypokalemia seen in this patient.

Humoral hypercalcemia of malignancy is most often driven by tumor secretion of PTH-related peptide (PTHrP), which binds the PTH receptor in bone and kidney, increasing osteoclastic bone resorption and renal calcium reabsorption. Initial management is volume repletion with isotonic saline to correct dehydration and improve renal calcium excretion, followed promptly by an intravenous bisphosphonate such as zoledronic acid, which inhibits osteoclast-mediated bone resorption and produces a sustained fall in calcium over 2-4 days. Calcitonin has a faster onset but a short-lived effect due to tachyphylaxis, so it is used as a bridge rather than definitive therapy. Loop diuretics are no longer recommended as first-line unless the patient develops fluid overload after adequate rehydration.

• A. Furosemide was historically used to promote calciuresis but is not recommended as routine therapy and may worsen volume depletion if given before adequate rehydration.
• B. Calcitonin acts quickly but its effect wanes within 48 hours due to tachyphylaxis, so it cannot serve as the main therapy.
• C. Cinacalcet lowers calcium by reducing PTH secretion via the calcium-sensing receptor and has no proven role in PTHrP-mediated malignancy hypercalcemia.

Periprocedural intravenous isotonic saline is the single most consistently effective and guideline-endorsed measure to prevent contrast-induced nephropathy, as it expands intravascular volume, improves renal medullary perfusion, and dilutes contrast within the tubules, reducing direct tubular toxicity and medullary hypoxia. Diabetic patients with reduced eGFR, as in this case, are at highest risk and benefit most from adequate hydration started before and continued after the procedure. N-acetylcysteine has not shown consistent benefit in randomized trials and is no longer routinely recommended. Diuretics before contrast can worsen volume depletion and increase nephrotoxic risk.

• B. N-acetylcysteine lacks consistent evidence of benefit in large trials and is not recommended as a primary preventive measure.
• C. Furosemide given before contrast can cause volume depletion and has been associated with increased, not decreased, risk of contrast nephropathy.
• D. Prophylactic dialysis has not been shown to prevent contrast nephropathy and is not standard practice for this indication.

Aminoglycosides accumulate in proximal tubular cells and cause direct toxic injury leading to tubular cell necrosis and sloughing, the hallmark of acute tubular necrosis. The classic urinary sediment finding in ATN is muddy brown granular casts, composed of degenerated tubular epithelial cells and Tamm-Horsfall protein, reflecting sloughed necrotic tubular cells within the cast matrix. This finding, combined with a rising creatinine after several days of nephrotoxic drug exposure and a FENa typically above 2%, confirms the diagnosis. White cell casts suggest interstitial nephritis or pyelonephritis, while red cell casts point to glomerular disease, neither of which fits this toxic tubular injury pattern.

• A. Red cell casts with dysmorphic erythrocytes indicate glomerulonephritis, not drug-induced tubular necrosis.
• B. White blood cell casts suggest acute interstitial nephritis or pyelonephritis, not toxic tubular injury.
• D. Isolated hyaline casts are a nonspecific finding and can occur in normal concentrated urine or prerenal states, not specifically ATN.

Rhabdomyolysis releases large amounts of myoglobin from damaged skeletal muscle into the circulation; myoglobin is filtered by the glomerulus and precipitates with Tamm-Horsfall protein in the distal tubule, especially in an acidic, concentrated urine environment, forming obstructing casts. Myoglobin also causes direct tubular epithelial toxicity through generation of reactive oxygen species and renal vasoconstriction. Aggressive intravenous isotonic fluid resuscitation is the cornerstone of management, aiming to maintain high urine output, flush out tubular casts, and prevent further ischemic injury; urine alkalinization may be considered as an adjunct to reduce myoglobin precipitation, though fluids remain primary. The dipstick-positive, microscopy-negative blood result is characteristic of myoglobinuria rather than true hematuria.

• A. Papillary necrosis is associated with analgesic abuse, diabetes, or sickle cell disease, not acute crush-related rhabdomyolysis, and stenting is not indicated.
• B. Immune complex glomerulonephritis is not the mechanism in crush injury-related rhabdomyolysis, and corticosteroids have no role here.
• D. Complement-mediated endothelial injury describes conditions like atypical hemolytic uremic syndrome, not rhabdomyolysis.

This patient's presentation of fever, rash, and acute kidney injury following a new antibiotic is classic for drug-induced acute interstitial nephritis, a type IV hypersensitivity reaction causing inflammatory infiltration of the renal interstitium. Eosinophiluria, best detected with Hansel or Wright stain on urine microscopy, supports the diagnosis, reflecting the eosinophil-rich interstitial infiltrate, though it is neither fully sensitive nor specific and a kidney biopsy remains the diagnostic gold standard in uncertain cases. White cell casts without significant hematuria or proteinuria further support a tubulointerstitial rather than glomerular process. Beta-lactam antibiotics and NSAIDs are among the most common causative agents of AIN.

• A. Dysmorphic red cells and red cell casts indicate glomerulonephritis, not interstitial nephritis.
• B. Fatty casts and heavy proteinuria are features of nephrotic syndrome, not acute interstitial nephritis.
• C. Granular casts with free epithelial cells are more typical of acute tubular necrosis rather than the hypersensitivity picture described here.

This patient's acute rise in creatinine with a palpable distended bladder and known BPH strongly suggests postrenal acute kidney injury from bladder outlet obstruction, which can progress to bilateral hydronephrosis if untreated. The immediate priority is urinary decompression through urethral catheterization, or suprapubic catheter placement if urethral catheterization fails, which relieves the obstruction and is both diagnostic and therapeutic, often leading to rapid improvement in renal function. Renal ultrasound can confirm hydronephrosis but should not delay catheterization when the clinical picture is clear. Diuretics and dialysis are inappropriate as initial steps because they do not address the underlying mechanical obstruction.

• A. Dialysis is not the first step; relieving the obstruction with catheterization usually resolves the AKI without need for dialysis.
• B. Diuretics do not relieve the obstruction and may worsen the situation by increasing bladder pressure against an obstructed outlet.
• C. Renal biopsy has no role in postrenal AKI and would not alter the immediate management of obstruction.

This patient has refractory hyperkalemia with ECG changes and severe metabolic acidosis that have not responded to medical therapy, both standard indications for emergent dialysis under the AEIOU criteria (Acidosis, Electrolyte abnormality, Intoxication, Overload, Uremia). Medical measures like calcium, insulin-dextrose, and beta-agonists are temporizing and do not remove potassium from the body. When these fail, definitive potassium removal requires hemodialysis. Delaying dialysis risks fatal arrhythmia.

• B. Repeating temporizing measures that already failed will not definitively lower potassium and wastes time in a life-threatening situation.
• C. Furosemide is ineffective in a patient who is oliguric from AKI and will not acutely correct life-threatening hyperkalemia or acidosis.
• D. Bicarbonate alone does not reliably lower potassium acutely and does not address the refractory hyperkalemia with ECG changes.

This patient meets diagnostic criteria for hepatorenal syndrome: cirrhosis with ascites, rise in creatinine without improvement after volume expansion with albumin and diuretic withdrawal, absence of shock, nephrotoxic drugs, or structural kidney disease, and no evidence of infection. First-line therapy is a splanchnic vasoconstrictor, terlipressin, combined with albumin, which improves renal perfusion by counteracting splanchnic vasodilation. Where terlipressin is unavailable, midodrine plus octreotide and albumin is an alternative. Liver transplantation remains the definitive treatment.

• B. Diuretics do not treat hepatorenal syndrome and can worsen renal perfusion by causing further volume depletion.
• C. TIPS is not first-line emergency therapy for hepatorenal syndrome and carries risk of hepatic encephalopathy in decompensated cirrhosis.
• D. There is no clinical or laboratory evidence of spontaneous bacterial peritonitis, so empirical antibiotics are not indicated here.

This child's presentation of heavy proteinuria (greater than 3.5 g/24h), hypoalbuminemia, and edema defines nephrotic syndrome, which results from podocyte injury increasing glomerular permeability to protein without significant glomerular inflammation. Nephritic syndrome, in contrast, is characterized by hematuria with red blood cell casts or dysmorphic red blood cells, hypertension, and only mild to moderate proteinuria, reflecting an inflammatory glomerular process with capillary wall disruption. The absence of hematuria and casts here supports a nephrotic rather than nephritic picture.

• A. This child is normotensive with heavy, not mild to moderate, proteinuria, making this feature inconsistent with the case.
• B. RBC casts indicate glomerular inflammation and bleeding, which is a nephritic feature not seen in this child's urinalysis.
• C. Dysmorphic RBCs and oliguria reflect a nephritic process, which is absent here as the urinalysis shows no red blood cells.

This girl's presentation, age, and laboratory findings (nephrotic-range proteinuria, normal complement, normal renal function, no hematuria or hypertension) are classic for minimal change disease, the most common cause of nephrotic syndrome in children aged 1 to 10 years. Children in this typical age group with a classic presentation do not require biopsy before treatment; empirical corticosteroid therapy is first-line, and the overwhelming majority achieve remission, which itself supports the diagnosis. Biopsy is reserved for atypical features, steroid resistance, or relapse requiring second-line therapy.

• A. Biopsy is unnecessary in a typical presentation at this age; steroid responsiveness itself confirms the diagnosis.
• B. Cyclophosphamide is reserved for steroid-resistant or frequently relapsing cases, not first-line therapy.
• D. ACE inhibitors reduce proteinuria but do not treat the underlying disease and are not sufficient as sole therapy for minimal change disease.

Serum anti-PLA2R antibody is positive in approximately 70-80% of cases of primary (idiopathic) membranous nephropathy and is now used as a specific serologic marker supporting the diagnosis without always requiring extensive secondary workup. Secondary causes of membranous nephropathy include hepatitis B infection, solid tumors, systemic lupus erythematosus, and certain drugs such as NSAIDs, and should be screened for based on clinical suspicion. In a patient with no risk factors for secondary causes, a positive anti-PLA2R result confirms primary disease and can guide immunosuppressive treatment decisions.

• A. Age-appropriate malignancy screening may be considered in secondary membranous nephropathy workup, but it does not confirm primary disease the way anti-PLA2R does.
• C. Protein electrophoresis screens for monoclonal gammopathy or amyloidosis, not for distinguishing primary membranous nephropathy.
• D. Hepatitis B is a recognized secondary cause of membranous nephropathy, but this patient has no risk factors or history suggesting hepatitis, making this less directly useful than anti-PLA2R.

This patient's recurrent episodes of gross hematuria occurring within 1-2 days of an upper respiratory tract infection, known as synpharyngitic hematuria, along with normal complement levels, are classic for IgA nephropathy, the most common primary glomerulonephritis worldwide. The rapid onset of hematuria closely following the infection distinguishes it from post-streptococcal glomerulonephritis, where hematuria typically develops 1-3 weeks after infection and is associated with low complement C3. Diagnosis is confirmed by renal biopsy showing mesangial IgA deposition, though the clinical pattern is highly suggestive.

• B. Membranoproliferative glomerulonephritis usually presents with low complement levels and a more insidious nephritic-nephrotic picture, not recurrent synpharyngitic hematuria.
• C. Alport syndrome is an inherited disorder presenting with persistent microscopic hematuria, sensorineural hearing loss, and family history, not episodic gross hematuria tied to infections.
• D. Post-streptococcal glomerulonephritis typically presents with a 1-3 week latency after infection and low complement levels, neither of which fits this case.

Post-streptococcal glomerulonephritis (PSGN) follows a latent period of 1-3 weeks after pharyngitis or impetigo, during which circulating immune complexes containing nephritogenic streptococcal antigens (such as NAPlr or SPEB) deposit subepithelially in the glomerulus, triggering complement activation via the alternative pathway. This produces transient hypocomplementemia (low C3) that normalizes within 6-8 weeks, a key diagnostic clue distinguishing PSGN from other glomerulonephritides. Management is supportive, with control of fluid overload and hypertension, as most children recover renal function fully. Persistently low C3 beyond 8 weeks should prompt evaluation for membranoproliferative glomerulonephritis or lupus nephritis.

• A. ANCA-associated vasculitis is pauci-immune (no immune complex deposits) and not linked to a preceding streptococcal infection with low C3.
• B. PSGN is immune-mediated, not due to direct bacterial invasion of the kidney.
• C. Linear anti-GBM deposition describes Goodpasture disease, which does not follow a latent period after infection.

Anti-GBM disease (Goodpasture syndrome) is caused by autoantibodies directed against the alpha-3 chain of type IV collagen in the glomerular and alveolar basement membranes, producing the combination of rapidly progressive glomerulonephritis and pulmonary hemorrhage. Biopsy characteristically shows crescents with linear IgG deposition along the GBM on immunofluorescence, distinguishing it from ANCA-associated vasculitis (pauci-immune, no significant immune deposits) and immune-complex diseases such as lupus nephritis (granular deposits) or IgA nephropathy (mesangial IgA deposits). Complement levels are typically normal in anti-GBM disease, unlike in lupus nephritis where C3/C4 are often low. Treatment requires urgent plasmapheresis plus cyclophosphamide and corticosteroids to remove and suppress pathogenic antibody production.

• A. IgA nephropathy shows mesangial IgA deposition, not linear anti-GBM antibody staining, and does not classically cause pulmonary hemorrhage.
• B. Lupus nephritis shows granular immune complex deposits and hypocomplementemia, not linear anti-GBM antibodies against collagen IV.
• C. Granulomatosis with polyangiitis is typically ANCA-positive and shows pauci-immune crescents without linear GBM deposition.

The biopsy findings of diffuse proliferative changes involving more than 50% of glomeruli with subendothelial deposits are diagnostic of ISN/RPS class IV lupus nephritis, the most severe and common proliferative form. Both class III (focal, under 50% of glomeruli) and class IV (diffuse, over 50%) lupus nephritis require aggressive induction immunosuppression, typically mycophenolate mofetil or intravenous cyclophosphamide combined with corticosteroids, to prevent progression to end-stage renal disease. Hydroxychloroquine is a baseline adjunct in all lupus nephritis classes but is not sufficient induction therapy alone. The histologic class, not clinical severity alone, is the primary determinant of induction regimen selection according to KDIGO lupus nephritis guidelines.

• A. Class II mesangial lupus nephritis lacks proliferative or crescentic features and this patient's biopsy shows diffuse proliferation involving the majority of glomeruli.
• B. Class VI represents advanced global glomerulosclerosis on biopsy, not active proliferative disease, and transplantation is not indicated at this creatinine level.
• D. Class V membranous lupus nephritis shows subepithelial deposits with a membranous pattern, not endocapillary proliferation, and requires immunosuppression beyond hydroxychloroquine alone.

The KDIGO classification stages CKD using two independent axes: eGFR category (G1-G5) and albuminuria category (A1-A3). An eGFR of 38 mL/min/1.73m² falls within the G3b range (30-44 mL/min/1.73m²), while a urine albumin-to-creatinine ratio of 350 mg/g (above 300 mg/g) falls within the A3 category (severely increased albuminuria). Combining both axes gives a classification of G3b A3, which carries a high risk of progression to kidney failure and cardiovascular events according to the KDIGO heat map. Persistence of abnormal findings on repeat testing over at least 3 months is required to confirm chronicity before assigning a CKD stage.

• B. G4 corresponds to eGFR 15-29 mL/min/1.73m² and A1 to albuminuria below 30 mg/g, both inconsistent with the given data.
• C. G3a corresponds to eGFR 45-59 mL/min/1.73m² and A2 to albuminuria 30-300 mg/g, neither of which matches this patient's eGFR of 38 or ACR of 350 mg/g.
• D. G2 corresponds to eGFR 60-89 mL/min/1.73m² and A2 to albuminuria 30-300 mg/g, neither of which matches this patient's values.

ACE inhibitors and ARBs reduce intraglomerular pressure and proteinuria in diabetic nephropathy by preferentially dilating the efferent arteriole, which can cause an expected initial rise in serum creatinine of up to 30% and mild hyperkalemia due to reduced aldosterone-mediated potassium excretion. A creatinine rise from 95 to 115 micromol/L (about 21%) and potassium of 5.6 mmol/L in an asymptomatic patient with no ECG changes are within the acceptable range to continue therapy with close monitoring, dietary potassium restriction, and repeat labs rather than stopping a renoprotective drug. Therapy should only be discontinued if creatinine rises more than 30% from baseline or if potassium rises to dangerous levels (generally above 6.0 mmol/L) or symptomatic hyperkalemia develops. This monitoring approach preserves the long-term benefit of RAAS blockade in slowing progression of diabetic kidney disease.

• B. Increasing the dose before reassessing renal function and potassium risks worsening hyperkalemia and acute kidney injury.
• C. Stopping lisinopril removes its proven renoprotective and anti-proteinuric benefit when the creatinine and potassium changes are still within an acceptable monitored range.
• D. Adding a potassium-sparing diuretic would worsen the existing hyperkalemia and is contraindicated in this setting.

As nephron mass declines, renal 1-alpha-hydroxylase activity falls, reducing conversion of 25-hydroxyvitamin D to active calcitriol. Lower calcitriol decreases intestinal calcium absorption and removes suppressive feedback on the parathyroid gland. Concurrently, declining GFR impairs phosphate excretion, and hyperphosphatemia directly stimulates parathyroid hormone secretion and parathyroid cell proliferation. The combination of hypocalcemia tendency, hyperphosphatemia, and low calcitriol drives secondary hyperparathyroidism in CKD-mineral bone disease.

• A. FGF-23 secretion actually increases in CKD as a compensatory response to phosphate retention, not decreases.
• C. CKD typically causes a tendency toward hypocalcemia, not hypercalcemia, due to reduced calcitriol-mediated intestinal absorption.
• D. This describes primary hyperparathyroidism, which is not driven by renal failure and would be associated with hypercalcemia.

This patient has hyperphosphatemia with coexisting hypercalcemia and evidence of vascular calcification, making calcium-based binders inappropriate because they would worsen the calcium burden and accelerate vascular calcification. Sevelamer is a non-calcium, non-aluminum polymer that binds intestinal phosphate without contributing to calcium load, making it preferred in patients with hypercalcemia, adynamic bone disease, or significant vascular calcification. Current KDIGO guidance recommends restricting calcium-based binder dose in such patients. Aluminum-based binders are avoided long-term due to the risk of aluminum toxicity and osteomalacia.

• A. Aluminum hydroxide is avoided for long-term use because of the risk of aluminum accumulation causing encephalopathy and bone disease.
• B. Calcium acetate carries the same risk of worsening hypercalcemia and vascular calcification as calcium carbonate.
• D. Calcium carbonate would raise serum calcium further and worsen vascular calcification in a patient already hypercalcemic.

This patient has absolute iron deficiency, indicated by a transferrin saturation below 20% and a low-normal ferritin, which is insufficient to support the erythropoiesis driven by an erythropoiesis-stimulating agent (ESA). KDIGO guidelines recommend correcting iron deficiency before or concurrently with starting an ESA, since erythropoiesis without adequate iron stores leads to poor response and requires higher ESA doses, increasing cardiovascular risk. Intravenous iron is preferred over oral iron in CKD patients, particularly pre-dialysis and dialysis patients, because gastrointestinal absorption of oral iron is unreliable in uremia. Starting an ESA without correcting iron deficiency first is a common cause of ESA hyporesponsiveness.

• B. Transfusion is not indicated for stable chronic anemia and should be reserved for symptomatic acute anemia or hemodynamic instability, also risking allosensitization in a transplant candidate.
• C. Oral iron is poorly absorbed in CKD patients due to uremia-related inflammation and elevated hepcidin, making intravenous iron the preferred route.
• D. Starting the ESA without correcting iron deficiency will result in a poor hematologic response and need for escalating doses.

Systemic non-steroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin-mediated afferent arteriolar vasodilation, reducing renal blood flow and glomerular filtration, which can precipitate acute kidney injury in patients with reduced renal reserve. In CKD stage 3b and beyond, oral NSAIDs should generally be avoided regardless of dose or duration, and alternatives such as topical NSAIDs, which have minimal systemic absorption, or cautious short-term opioid use are preferred. Adding a proton pump inhibitor protects against gastrointestinal bleeding but does nothing to prevent NSAID-induced renal hemodynamic injury. Monitoring creatinine after starting an NSAID identifies harm after it has occurred rather than preventing it.

• A. A proton pump inhibitor addresses gastrointestinal risk but provides no protection against NSAID-induced reduction in renal perfusion.
• C. Monitoring creatinine is reactive rather than preventive and does not justify exposing this patient to an avoidable nephrotoxic risk.
• D. Even at low doses and short duration, oral NSAIDs carry significant risk of acute kidney injury in CKD stage 3b or worse and should be avoided, not merely minimized.

Indications for initiating chronic dialysis include uremic symptoms such as persistent nausea and anorexia, refractory fluid overload with pulmonary and peripheral edema unresponsive to diuretics, and biochemical abnormalities such as hyperkalemia and metabolic acidosis that are refractory to medical therapy. This patient meets multiple indications simultaneously despite optimized conservative management, making further medical titration inappropriate and dialysis initiation the correct next step. Delaying dialysis in this setting risks progression to life-threatening complications such as pulmonary edema or cardiac arrhythmia from hyperkalemia. Chronic dialysis should be started based on clinical and biochemical indications rather than a fixed GFR threshold alone.

• A. Escalating diuretic therapy is unlikely to be effective given the severity of fluid overload and uremic symptoms already present, and delays definitive treatment.
• B. This is an acute stabilizing measure for severe hyperkalemia with ECG changes, not a definitive long-term solution for this patient's overall refractory uremic state.
• D. His metabolic acidosis and uremic symptoms are already refractory to oral bicarbonate and conservative measures, making further observation inappropriate.

An arteriovenous (AV) fistula is the preferred vascular access for hemodialysis because it has the lowest rates of infection, thrombosis, and long-term failure compared with grafts or catheters. Fistulas require several weeks to months to mature adequately for cannulation, so early referral, ideally when estimated GFR falls below 20 mL/min/1.73m² or dialysis is anticipated within 6-12 months, is recommended to avoid starting dialysis with a catheter. Catheters carry the highest risk of bloodstream infection and central vein stenosis and should be reserved for urgent dialysis initiation when no mature access is available. Grafts are considered only when a patient's vasculature is unsuitable for fistula creation.

• A. Waiting until stage 5 CKD with uremic symptoms does not allow adequate time for fistula maturation and risks starting dialysis via catheter.
• B. Grafts are reserved for patients with inadequate vasculature for a fistula; this patient has good quality veins favoring fistula creation.
• C. Catheters have the highest complication rates including infection and central venous stenosis and should not be the planned long-term access when a fistula is feasible.

Peritoneal dialysis-associated peritonitis is diagnosed when effluent white cell count exceeds 100 cells/µL with at least 50% neutrophils, in the setting of cloudy fluid and abdominal pain. The International Society for Peritoneal Dialysis recommends starting empiric intraperitoneal antibiotics immediately after sending the fluid for cell count, Gram stain, and culture, without waiting for culture confirmation, because delayed treatment increases the risk of catheter loss and technique failure. Empiric coverage should include both gram-positive organisms (such as a first-generation cephalosporin or vancomycin) and gram-negative organisms (such as a third-generation cephalosporin or an aminoglycoside), then narrowed once culture results return. Catheter removal is reserved for refractory, relapsing, or fungal peritonitis, not as an initial step.

• A. Treatment must not be delayed pending culture results, as this increases the risk of catheter loss and systemic sepsis.
• B. Catheter removal is reserved for refractory or relapsing peritonitis, or fungal infection, not for a first presumptive bacterial episode before culture results.
• D. Empiric antifungal therapy is not indicated unless fungal peritonitis is suspected or confirmed, such as after prior antibiotic courses or culture evidence of fungi.

Dialysis disequilibrium syndrome occurs when hemodialysis rapidly lowers plasma urea, but urea clearance from brain tissue lags behind because of the blood-brain barrier, creating a transient osmotic gradient. Water then shifts into brain cells, causing cerebral edema and raised intracranial pressure, which manifests as headache, nausea, confusion, or seizures. It is most common in patients with very high pre-dialysis urea starting their first session, and is prevented by using a lower blood flow rate and shorter dialysis time initially. Treatment is supportive, including slowing or stopping dialysis and giving mannitol if severe.

• A. Intradialytic hypotension can cause similar symptoms but the vital signs here are stable, making an osmotic mechanism more likely.
• B. Hypoglycemia is not a typical dialysis complication and is not supported by the clinical picture described.
• D. Heparin-associated bleeding would present with focal deficits or signs of hemorrhage, not a global picture of headache and confusion from osmotic shift.

Calcineurin inhibitor nephrotoxicity presents with a rise in creatinine accompanied by a supratherapeutic tacrolimus level, tremor, and hypertension, reflecting afferent arteriolar vasoconstriction rather than immune-mediated injury. Unlike acute rejection, the urinalysis is typically bland without cellular casts or significant proteinuria. The first step is dose reduction with a trough level recheck, since toxicity is often reversible. Biopsy is reserved for cases where the diagnosis remains unclear after addressing a clearly elevated drug level, or when creatinine fails to improve.

• A. Biopsy is invasive and not the immediate next step when a clearly supratherapeutic drug level and compatible clinical picture point to toxicity.
• C. Switching regimens without confirming the response to dose reduction is premature and skips the reversible, lower-risk intervention.
• D. Increasing immunosuppression is inappropriate when toxicity rather than rejection is the likely cause, and could worsen nephrotoxicity.

Hyperacute rejection occurs within minutes to hours of transplantation due to preexisting recipient antibodies, usually from prior transfusions, pregnancies, or transplants, that bind donor ABO or HLA antigens on vascular endothelium. This triggers complement activation, endothelial damage, and widespread microvascular thrombosis, leading to graft mottling and immediate cessation of function. It is now rare because of routine pre-transplant crossmatching. In contrast, acute rejection is T-cell mediated and occurs over days to weeks, while chronic rejection develops over months to years through fibrointimal changes.

• A. Chronic allograft changes develop over months to years and would not explain an immediate intraoperative event.
• C. T-cell mediated injury describes acute rejection, which develops over days to weeks, not minutes.
• D. Calcineurin inhibitor toxicity is a drug adverse effect, not the mechanism of immediate graft thrombosis seen here.

BK virus nephropathy typically presents 3 to 12 months post-transplant with an asymptomatic, gradual rise in creatinine in a patient without systemic infectious symptoms. Decoy cells on urine cytology, representing renal tubular cells with viral intranuclear inclusions, are a key screening clue, and diagnosis is confirmed by plasma BK viral load and allograft biopsy showing characteristic inclusion bodies with tubulointerstitial inflammation. Management is primarily reduction of immunosuppression, since no specific antiviral therapy is proven effective. CMV disease, by contrast, usually presents with fever, leukopenia, and organ-specific symptoms such as colitis or pneumonitis, typically within the first 1 to 6 months, especially in CMV-mismatched recipients.

• A. Pyelonephritis typically causes fever, flank pain, and pyuria with bacteria, not decoy cells.
• C. Pneumocystis pneumonia presents with respiratory symptoms and hypoxia, not isolated asymptomatic creatinine rise with decoy cells.
• D. CMV colitis would present with fever, diarrhea, and gastrointestinal symptoms, which are absent here.

Non-contrast CT of the abdomen and pelvis is the imaging study of choice for suspected acute renal colic because of its high sensitivity and specificity for detecting ureteric and renal stones of nearly any composition, as well as for identifying the size, location, and degree of obstruction. It also helps exclude alternative diagnoses such as appendicitis or abdominal aortic aneurysm. Ultrasound is preferred in pregnant patients or children to avoid radiation but is less sensitive for small or mid-ureteric stones. Intravenous pyelography has largely been replaced by CT due to lower sensitivity and the need for contrast.

• A. Ultrasound has lower sensitivity for ureteric stones and is generally reserved for pregnant patients or children.
• C. Intravenous pyelography has been largely replaced by CT due to lower sensitivity and contrast exposure.
• D. Plain X-ray misses radiolucent stones such as uric acid stones and has lower overall sensitivity.

Idiopathic hypercalciuria with normal serum calcium and parathyroid hormone is a common cause of recurrent calcium oxalate stones. Management includes high fluid intake to maintain dilute urine, dietary sodium restriction because high sodium intake increases urinary calcium excretion, and thiazide diuretics, which reduce urinary calcium by enhancing distal tubular calcium reabsorption. Dietary calcium restriction is not recommended, as it can paradoxically increase oxalate absorption and stone risk by reducing intestinal oxalate binding.

• A. Increasing oxalate intake would worsen stone risk, and this patient's oxalate level is already normal.
• C. Dietary calcium restriction is avoided, and loop diuretics increase urinary calcium excretion, worsening hypercalciuria.
• D. Fluid restriction increases urinary stone-forming solute concentration, raising stone risk, and allopurinol is used for uric acid stones.

Struvite (magnesium ammonium phosphate) stones form in the setting of chronic urinary tract infection with urease-producing organisms such as Proteus mirabilis, Klebsiella, or Providencia. Bacterial urease hydrolyzes urinary urea into ammonia and carbon dioxide, which raises the urine pH into the alkaline range and promotes precipitation of magnesium ammonium phosphate along with calcium carbonate-apatite. These stones can grow rapidly to fill the renal pelvis and calyces, forming a staghorn calculus, and typically require complete surgical removal combined with treatment of the underlying infection to prevent recurrence.

• A. Metabolic acidosis would increase citrate excretion variably but does not explain alkaline urine or urease-producing infection.
• B. Increased oxalate absorption causes calcium oxalate stones and does not require urease-producing bacterial infection.
• C. Hyperuricosuria causes uric acid stones, which form in acidic urine, not the alkaline urine seen here.

Uric acid stones form in the setting of persistently acidic urine (pH less than 5.5) and are associated with conditions of high purine turnover such as gout, obesity, and metabolic syndrome. Unlike calcium-containing stones, they are radiolucent on plain X-ray but visible on CT. A key feature is that uric acid stones can dissolve with urinary alkalinization, typically using oral potassium citrate or sodium bicarbonate to raise urine pH to 6.5-7.0, which increases the solubility of uric acid. Allopurinol may be added if hyperuricosuria persists despite alkalinization.

• A. Vitamin C can increase urinary oxalate and is not used to dissolve uric acid stones.
• B. Acetazolamide further acidifies urine in some contexts but is not the standard agent; alkalinization, not acidification, is needed here.
• C. Calcium restriction is relevant to calcium stone prevention, not uric acid stone dissolution.

An obstructing stone with signs of infection (fever, tachycardia, hypotension) constitutes a urological emergency because the combination of obstruction and infection can rapidly progress to urosepsis and pyonephrosis. The priority is urgent decompression of the collecting system, achieved by either percutaneous nephrostomy or retrograde ureteral stenting, combined with broad-spectrum antibiotics. Definitive stone removal (ureteroscopy or lithotripsy) is deferred until the infection has resolved. Early decompression reduces intrarenal pressure, allows source control of infected urine, and prevents progression to septic shock.

• A. Lithotripsy fragments the stone but does not relieve obstruction and can worsen sepsis by releasing bacteria.
• B. Medical expulsive therapy is inappropriate when infection complicates obstruction; it delays decompression.
• D. Definitive endoscopic stone removal should be deferred until the infection is controlled and decompression achieved.

Lithium accumulates in collecting duct principal cells and interferes with aquaporin-2 trafficking, making the collecting duct unresponsive to antidiuretic hormone. During water deprivation, urine fails to concentrate appropriately, and administration of exogenous desmopressin produces little or no further rise in urine osmolality because the defect is at the receptor/aquaporin level, not hormone deficiency. This pattern confirms nephrogenic rather than central diabetes insipidus, where desmopressin would significantly increase urine osmolality. Management includes lithium dose reduction if possible, adequate hydration, and amiloride, which blocks lithium entry into collecting duct cells.

• A. Primary polydipsia shows a rise in urine osmolality with water deprivation as endogenous ADH is appropriately suppressed and then released.
• B. In central DI, desmopressin administration causes a significant rise in urine osmolality because the kidney can still respond to ADH.
• C. SIADH presents with hyponatremia and inappropriately concentrated urine, not hypernatremia with dilute urine.

Fibromuscular dysplasia is a non-atherosclerotic, non-inflammatory arteriopathy that predominantly affects young women and classically produces a 'string of beads' appearance on angiography due to alternating areas of medial thinning and fibrous ridges, typically in the mid to distal renal artery. It is a common cause of secondary hypertension in young patients without other cardiovascular risk factors. In contrast, atherosclerotic renal artery stenosis typically occurs in older patients with risk factors such as diabetes, smoking, and hyperlipidemia, and affects the proximal renal artery and ostium. Treatment of symptomatic fibromuscular dysplasia often includes percutaneous balloon angioplasty, which has excellent outcomes in this population.

• B. Takayasu arteritis typically affects the aorta and its major branches with systemic inflammatory features and elevated inflammatory markers, which are not described here.
• C. Renal vein thrombosis presents with flank pain, hematuria, and often nephrotic syndrome, not hypertension with a beaded arterial pattern.
• D. Atherosclerotic disease typically occurs in older patients with vascular risk factors and affects the proximal artery and ostium, not this young woman's distal beaded pattern.

This child's presentation of bloody diarrhea from Shiga toxin-producing E. coli O157:H7 followed by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury is classic for Shiga toxin-associated hemolytic uremic syndrome, the most common cause of acute kidney injury in previously healthy children. Shiga toxin damages glomerular endothelial cells, triggering platelet activation and microthrombi formation that mechanically fragment red cells into schistocytes. Normal ADAMTS13 activity excludes thrombotic thrombocytopenic purpura, where severe deficiency of this von Willebrand factor-cleaving protease is diagnostic. Management is supportive, including careful fluid and electrolyte management and dialysis if needed; antibiotics and antimotility agents are avoided as they may increase the risk of hemolytic uremic syndrome or worsen toxin release.

• A. DIC is driven by widespread activation of the coagulation cascade with abnormal PT/aPTT and low fibrinogen, not an isolated microangiopathy following diarrheal illness.
• B. Atypical HUS results from complement dysregulation and is not preceded by Shiga toxin-producing bacterial diarrhea.
• D. TTP is characterized by severely reduced ADAMTS13 activity, which is normal here, and typically occurs in adults without a preceding diarrheal illness.

The renal medulla is normally an area of low oxygen tension, high osmolality, and sluggish blood flow in the vasa recta, conditions that promote red cell sickling even in patients with sickle trait or disease. Recurrent microvascular occlusion and ischemia in this region leads to papillary necrosis, presenting with hematuria and flank pain, and progressively damages the countercurrent multiplication system, producing isosthenuria, the inability to concentrate or dilute urine appropriately. This explains why sickle cell patients are at risk of dehydration and why their urine osmolality remains relatively fixed near plasma osmolality despite fluid restriction. Hydroxyurea and adequate hydration help reduce sickling-related complications, though established papillary necrosis is often irreversible.

• B. Amyloidosis causes nephrotic-range proteinuria from glomerular deposition, not isosthenuria or papillary necrosis.
• C. Immune complex deposition causes glomerular disease with proteinuria and an active urinary sediment, not papillary necrosis from vascular occlusion.
• D. Papillary necrosis in sickle cell disease is due to vaso-occlusion and ischemia, not direct infection, though pyelonephritis is a differential diagnosis to exclude.

This patient has hypertensive emergency with end-organ damage (hypertensive retinopathy, encephalopathy, and likely renal involvement). Treatment requires a titratable intravenous agent such as labetalol or nicardipine, with a controlled reduction of mean arterial pressure by no more than 25% in the first hour to avoid precipitating cerebral, renal, or coronary hypoperfusion. Oral agents have unpredictable onset and duration and are unsuitable for emergencies. Rapid normalization of blood pressure can cause ischemic stroke or watershed infarction because autoregulation has shifted to a higher pressure range.

• A. Furosemide does not reliably or safely control blood pressure acutely and does not allow controlled titration.
• B. Oral agents have delayed and unpredictable onset, unsuitable for emergencies with end-organ damage.
• C. Sublingual nifedipine causes uncontrolled, precipitous drops in blood pressure and risks ischemic events.

Spironolactone is a competitive aldosterone receptor antagonist acting on the principal cells of the collecting duct. By blocking aldosterone's effect, it reduces sodium reabsorption and, consequently, potassium and hydrogen secretion, producing a potassium-sparing diuretic effect. When combined with an ACE inhibitor, which already reduces aldosterone production, the risk of hyperkalemia is substantially increased, requiring close monitoring of serum potassium and renal function after initiation. This combination is used for mortality benefit in heart failure with reduced ejection fraction but mandates careful laboratory follow-up.

• A. This describes the mechanism of acetazolamide, not spironolactone.
• B. This describes amiloride or triamterene, which act directly on sodium channels independent of aldosterone.
• D. This describes the mechanism of loop diuretics, not spironolactone.

Pyelonephritis in pregnancy is managed differently from uncomplicated cystitis: it requires hospital admission for intravenous antibiotics and supportive care, particularly when the patient has systemic symptoms, fever, or is unable to tolerate oral intake, because of risks to both mother and fetus including preterm labor and sepsis. A third-generation cephalosporin such as ceftriaxone is a safe and effective first-line choice in pregnancy. Fluoroquinolones are avoided in pregnancy due to concerns about fetal cartilage and musculoskeletal development. Oral regimens and short-course or single-dose therapy are reserved for uncomplicated lower urinary tract infection, not pyelonephritis.

• A. Fosfomycin single-dose therapy is used for uncomplicated cystitis, not pyelonephritis, and oral therapy is unsuitable given vomiting.
• C. Oral therapy at home is inappropriate for pyelonephritis with systemic toxicity and vomiting; nitrofurantoin also does not achieve adequate tissue levels for pyelonephritis.
• D. Fluoroquinolones are generally avoided in pregnancy due to potential fetal cartilage toxicity.

Asymptomatic bacteriuria in pregnancy is treated because of the significantly increased risk of progression to pyelonephritis, preterm labor, and low birth weight, so all pregnant women are screened and treated if bacteriuria is confirmed. In contrast, asymptomatic bacteriuria in healthy nonpregnant adults, including older women, does not require antibiotic treatment because treatment does not reduce symptomatic infection rates and instead promotes antimicrobial resistance and adverse drug effects. Exceptions to this nonpregnant rule include patients undergoing urologic procedures with expected mucosal trauma. Screening and treatment thresholds therefore differ markedly based on pregnancy status.

• A. This reverses the correct management; pregnancy, not older age, is the indication for treating asymptomatic bacteriuria.
• B. Pregnant women with asymptomatic bacteriuria do require treatment due to risk of ascending infection and obstetric complications.
• C. Treating all asymptomatic bacteriuria regardless of pregnancy status contradicts guidelines and promotes resistance.

Dysmorphic red blood cells, which show irregular membrane contours and blebs from passage through the damaged glomerular basement membrane and tubules, along with red blood cell casts formed by erythrocytes becoming trapped in Tamm-Horsfall protein within the tubules, are specific markers of glomerular bleeding. Lower urinary tract bleeding, such as from cystitis, stones, or tumors, typically produces isomorphic (uniformly round) red blood cells and does not form casts, since the cells enter the urine after the tubular system. Blood clots are characteristic of lower tract or collecting system bleeding, as glomerular bleeding rarely produces clots due to the presence of urokinase and anticoagulant factors in tubular fluid. This patient's presentation, with recent infection, hematuria, proteinuria, casts, and hypertension, is consistent with acute glomerulonephritis.

• A. Terminal hematuria localizes bleeding to the bladder neck or prostatic urethra, a lower tract source.
• B. Clots suggest a lower urinary tract or structural source, as glomerular bleeding rarely clots in the urinary tract.
• C. Isolated hematuria without proteinuria or casts is more typical of a lower urinary tract source, such as stones or tumors.

A mentally competent adult has the right to accept or refuse medical treatment after being adequately informed, and this autonomy takes precedence over family wishes. Confidentiality also means the physician cannot disclose the patient's medical information to relatives without his consent, even if they are close family members. The family's concern does not override the patient's legal and ethical right to self-determination. Physicians should continue to counsel the patient and explore his reasons for refusal, but coercion or deception is not permitted.

• A. Court intervention is not warranted when a competent patient makes an informed, voluntary refusal of treatment.
• B. Withholding diagnosis from a competent patient at the family's request breaches his right to information and autonomy.
• C. Family consent cannot substitute for the decision of a mentally competent adult patient.