Types of hematuria and patient routing
Gross hematuria (macroscopic haematuria) is visible to the naked eye and serves as a strong predictor of serious urological diseases. With persistent symptoms even after initially negative tests, cancer is found in 17% of cases.
Microscopic hematuria (microscopic haematuria) requires confirmation under a microscope. Relying solely on urine dipstick testing is unacceptable: free hemoglobin and myoglobin frequently yield false-positive results. Screening asymptomatic young patients has low value (less than 2% pathology detection rate).
Where to refer the patient?
- To a nephrologist: if there are signs of glomerular or tubular damage (arterial hypertension, elevated creatinine, red blood cell casts, proteinuria).
- To a urologist: if an epithelial source is suspected. Referral is mandatory for patients with symptoms, gross hematuria, or cancer risk factors (smoking, benzene exposure, pelvic irradiation, analgesic abuse).
Causes: stones and calcifications
Non-glomerular hematuria is divided into renal (tumors, infarctions, polycystic kidney disease, tuberculosis) and extrarenal (prostate cancer, cystitis, coagulopathies, trauma).
A frequent cause of hematuria is nephrolithiasis (nephrolithiasis). Most stones (calcium oxalates and phosphates) are radiopaque. About 15% are struvite stones, which grow in alkaline urine in the presence of infection. Uric acid and xanthine stones (5%) are not visible on standard radiography.
Pathological calcification of the parenchyma is termed nephrocalcinosis (nephrocalcinosis). In 95% of cases, it affects the medulla (e.g., in hyperparathyroidism or medullary sponge kidney). On ultrasound, it appears as focal echogenicity enhancement, and on radiography as a speckled pattern.
CT in the diagnosis of urolithiasis and neoplasms
The gold standard for detecting calculi is unenhanced computed tomography. It detects 98% of stones, whereas ultrasound detects only 40% (ultrasound tends to overestimate size and miss small stones). The density of a typical stone on CT ranges from 150 to 1000 HU. Low-dose CT (~20% of standard radiation dose) is acceptable for stone detection.
Multiphasic contrast-enhanced CT is used for tumor diagnosis:
- Unenhanced: detection of calcifications or fat in angiomyolipomas.
- Corticomedullary: evaluation of angiogenesis, recognition of pseudotumors.
- Nephrographic: most urothelial tumors show maximum visualization in this phase.
A reliable sign of a tumor is contrast enhancement with a difference of more than 20 HU between the unenhanced and nephrographic phases. A difference of 10–20 HU is considered indeterminate.
CT urography and MRI capabilities
CT urography (CTU) outperforms traditional methods (intravenous urography and ultrasound) in evaluating hematuria. In diagnosing transitional cell carcinoma, sensitivity reaches 0.97 and specificity 0.93. However, the positive predictive value (PPV) is only 0.79, so histological confirmation is mandatory prior to surgical intervention.
If CT has difficulty differentiating oncocytoma from malignant renal cell carcinoma, MRI can be helpful. Apparent diffusion coefficient (ADC) measurement and multiphasic perfusion demonstrate high accuracy, although the method still requires final validation for routine clinical practice.
Briefly: answers to topical questions
What are the main differences between renal and extrarenal non-glomerular hematuria?
The main differences lie in the etiological factors causing the bleeding.
| Etiology | Renal causes (Renal) | Extrarenal causes (Extrarenal) |
|---|---|---|
| Tumors | Renal cell carcinoma, angiomyolipoma, oncocytoma | Prostate cancer, BPH |
| Infectious Diseases | Pyelonephritis, cytomegalovirus, mononucleosis | Cystitis, prostatitis, schistosomiasis, condylomata |
| Other | Vascular, metabolic, familial diseases | Stones, coagulopathies, trauma, medications |
Transitional cell carcinoma and tuberculosis can have either a renal or extrarenal location.
What is the probability of spontaneous passage of calculi of various sizes?
The probability of spontaneous stone passage depends on its size:
- Calculi 2–4 mm — 76%.
- Calculi 5–7 mm — 60%.
- Calculi 7–9 mm — 48%.
- Calculi > 9 mm — 20%.
The degree of perirenal fat stranding inversely correlates with the probability of spontaneous stone passage.
What are the referral criteria for a urologist according to the AUA rule?
Referral criteria depend on the presence of symptoms and risk factors for malignancies.
- Asymptomatic patients — referral is indicated only if there are more than 3 erythrocytes per high-power field in 2 out of 3 urinalyses.
- Mandatory referral — required in cases of symptomatic microscopic hematuria, gross hematuria, and elevated risk of urological malignancies.
Risk factors include smoking, exposure to benzene or aromatic amines, irritative symptoms, refractory urinary tract infections, pelvic irradiation, and analgesic abuse.
A simple patient routing rule for hematuria: Proteinuria, casts, and hypertension — the patient goes to a nephrologist. Everything else (stones, infections, oncology) — to a urologist.
Class and exam questions
Can hematuria be ruled out using test strips alone?
No. Test strips frequently yield false-positive results (in 75% of cases) due to myoglobin or free hemoglobin. The diagnosis requires mandatory confirmation under a microscope.
Which kidney stones are invisible on a standard plain radiogram?
Uric acid and xanthine stones (about 5% of all stones) are radiolucent. On unenhanced CT, indinavir stones are an exception — they may also be invisible.
How to distinguish true contrast enhancement by a tumor from an artifact on CT?
True enhancement is defined as a density difference of more than 20 HU between the unenhanced and nephrographic phases. Artificial density elevation is frequently seen in cysts and is termed pseudoenhancement.
Is a biopsy mandatory when cancer is detected on CT urography?
Yes. Although CT urography has high sensitivity, its positive predictive value (PPV) is 0.79. The diagnosis must be histologically confirmed prior to surgery.
What else to study on this topic
- Clinical and radiological distinctions between medullary and cortical nephrocalcinosis
- An algorithm for stratifying hematuria patients into high- and low-risk groups prior to CT urography
- The role of diffusion-weighted MRI in differentiating oncocytoma from renal cell carcinoma
- Analysis of extrarenal causes of hematuria: medication-related factors and coagulopathies
- Predicting spontaneous ureteral stone passage based on CT data
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