What is Hematuria?
Hematuria is the presence of blood in the urine, defined microscopically as ≥3 red blood cells per high-power field on urinalysis, and it represents a common clinical finding that can signal conditions ranging from benign causes to life-threatening malignancies requiring urgent evaluation. 1
Classification of Hematuria
Hematuria is categorized into two main types based on visibility:
- Gross (Macroscopic) Hematuria: Blood visible to the naked eye, appearing as red, pink, or tea-colored urine depending on the source 1, 2
- Microscopic Hematuria: Blood detectable only under microscopic examination, defined as ≥3 RBCs per high-power field 1, 2
The distinction between these two presentations is clinically critical, as gross hematuria carries a substantially higher risk of underlying malignancy (>10% and up to 30-40% in some series) compared to microscopic hematuria (0.5-5% risk) 1, 3
Common Causes of Hematuria
Urologic Causes
- Malignancy: Bladder cancer, renal cell carcinoma, and urothelial cancers represent the most concerning etiologies, particularly in adults over 35 years with risk factors 2, 3
- Urinary Tract Infection: One of the most common benign causes of both microscopic and gross hematuria 2, 3
- Urolithiasis: Kidney and ureteral stones typically present with painful hematuria and flank pain 1, 2
- Benign Prostatic Hyperplasia: A frequent cause of hematuria in older men 2, 4
- Trauma: Injury to the kidneys or lower urinary tract 2
Renal/Glomerular Causes
- Glomerulonephritis: Including post-infectious GN and IgA nephropathy, characterized by dysmorphic RBCs (>80%), red cell casts, and proteinuria 2, 5
- Alport Syndrome: Hereditary nephritis with associated hearing loss 2
- Thin Basement Membrane Nephropathy: An autosomal dominant condition causing chronic kidney disease 2
Other Causes
- Vigorous Exercise: Can cause transient hematuria that resolves spontaneously 2
- Medications: Anticoagulants and antiplatelet agents may unmask underlying pathology but do not themselves cause hematuria 1, 2
- Menstrual Contamination: Can lead to false-positive results in women 2
Clinical Significance and Risk Stratification
The color and character of urine provide diagnostic clues:
- Tea-colored urine suggests a glomerular source of bleeding 2
- Painless gross hematuria has a stronger association with malignancy than hematuria accompanied by flank pain or renal colic 1
- Symptomatic gross hematuria with flank pain is the classic presentation of urinary stone disease 1
A critical pitfall is attributing hematuria solely to anticoagulation therapy—these medications do not cause hematuria but may reveal underlying pathology that requires full evaluation. 1, 2
Prevalence and Population Considerations
- Asymptomatic microscopic hematuria occurs in 0.9-18% of the adult population 1
- Risk factors for malignancy include male gender, age >35 years, smoking history (especially >30 pack-years), and occupational exposure to chemicals or dyes 2, 6
- In children, glomerulonephritis and congenital anomalies are more common causes 2
Key Clinical Principle
Gross hematuria should never be ignored and requires urgent urologic referral even if self-limited, given the consistently high pretest probability of cancer or other clinically significant conditions. 1, 2, 7