What are the causes of microhematuria?

Causes of Microhematuria

The most common causes of microhematuria include malignancy, infection, inflammation, calculus disease, benign prostatic hyperplasia (BPH), and congenital or acquired anatomic abnormalities of the urinary tract. 1

Urologic Causes

• Malignancy: Accounts for 2.6-4% of microscopic hematuria cases, with risk increasing based on age, smoking history, and degree of hematuria 2, 3
• Urinary Tract Infection: Common cause of both microscopic and macroscopic hematuria that should resolve with appropriate antibiotic treatment 2, 4
• Urolithiasis (kidney and ureteric stones): Can cause painful hematuria and is a common benign cause 2, 5
• Benign Prostatic Hyperplasia (BPH): Common cause in men, especially older men 2, 3
• Trauma: Injury to the kidneys or lower urinary tract can result in hematuria 2
• Congenital or acquired anatomic abnormalities: Various structural issues in the urinary tract can lead to microhematuria 1

Renal/Glomerular Causes

• Glomerulonephritis: Including post-infectious and IgA nephropathy 2
• Alport Syndrome: Hereditary nephritis often associated with hearing loss 2
• Thin Basement Membrane Nephropathy: An autosomal dominant condition that can cause progressive chronic kidney disease 2
• Interstitial Renal Disease: Including drug-induced interstitial disease or analgesic nephropathy 2
• Other nephropathies: Such as lupus nephritis and vasculitis 2

Systemic/Other Causes

• Vigorous exercise: Can cause transient hematuria that resolves with rest 2, 6
• Menstruation: Can contaminate urine samples in women, leading to false-positive results 2, 6
• Medications: Anticoagulants and antiplatelet agents may unmask underlying pathology but do not directly cause hematuria 2, 3
• Coagulopathies: Such as hemophilia can cause hematuria due to bleeding disorders 2
• Sickle Cell Disease: Can cause hematuria due to renal papillary necrosis 2

Risk Stratification for Malignancy

The AUA/SUFU guidelines stratify patients with microhematuria into risk categories based on:

• Degree of hematuria:

  • Low risk: 3-10 RBC/HPF
  • Intermediate risk: 11-25 RBC/HPF
  • High risk: >25 RBC/HPF 1

• Age:

  • For women: <60 years (low risk), ≥60 years (intermediate risk)
  • For men: <40 years (low risk), 40-59 years (intermediate risk), ≥60 years (high risk) 1

• Smoking history:

  • Low risk: Never smoker or <10 pack years
  • Intermediate risk: 10-30 pack years
  • High risk: >30 pack years 1

Important Clinical Considerations

• Gross hematuria has a higher association with malignancy (30-40%) compared to microscopic hematuria (2.6-4%) 2, 7
• Dysmorphic red blood cells and red cell casts suggest glomerular bleeding (>80% dysmorphic RBCs indicates glomerular source) 2
• Significant proteinuria accompanying hematuria suggests renal parenchymal disease 2
• Tea-colored urine suggests a glomerular source of hematuria 2
• Anticoagulation therapy is not a reason to forgo evaluation of hematuria 2, 3
• "Idiopathic microscopic hematuria" without an obvious underlying medical condition accounts for approximately 80% of patients with asymptomatic hematuria 8

Diagnostic Approach

• Confirm microscopic hematuria with ≥3 RBCs per high-power field on properly collected specimen 4
• Assess for risk factors for urologic malignancy (age >35 years, smoking history, degree of hematuria) 1, 3
• Evaluate for benign causes including infection, BPH, and urolithiasis 9, 4
• Determine if hematuria is glomerular (dysmorphic RBCs, proteinuria) or non-glomerular 2
• Patients with persistent hematuria after negative initial evaluation should have repeat urinalysis at 6,12,24, and 36 months 3
• Consider nephrology referral if hematuria persists with development of hypertension, proteinuria, or evidence of glomerular bleeding 2, 3