How do I confirm hematuria (blood in the urine) in a patient with internal bleeding and large amounts of blood in their urine?

Confirming Hematuria (Blood in the Urine)

To confirm large amounts of blood in the urine, you must perform microscopic urinalysis showing ≥3 red blood cells per high-power field (RBC/HPF) on a properly collected clean-catch midstream urine specimen—never rely on dipstick testing alone, as it has only 65-99% specificity and can produce false positives. 1

Initial Confirmation Steps

Visual Assessment

• Verify that you are seeing actual blood by directly observing the urine specimen—gross (macroscopic) hematuria is characterized by visible blood that can be seen with the naked eye 1
• Exclude pseudohematuria by ruling out food substances (beets, blackberries) or medications (rifampin, phenazopyridine) that can color urine red without containing actual red blood cells 1, 2

Microscopic Confirmation (Mandatory)

• Obtain microscopic urinalysis to confirm ≥3 RBCs per high-power field on at least two of three properly collected clean-catch midstream specimens 1, 2
• Do not proceed with extensive workup based solely on dipstick positivity, as the American Urological Association explicitly states that "a dipstick reading suggestive of hematuria should not lead to imaging or further investigation without confirmation of three or greater red blood cells per high power field" 1

Distinguishing Glomerular from Non-Glomerular Sources

Urine Characteristics

• Tea-colored or cola-colored urine strongly suggests a glomerular source of bleeding 1, 2
• Bright red blood suggests lower urinary tract bleeding (bladder, urethra, prostate) 1

Microscopic Examination

• Examine urinary sediment for dysmorphic RBCs using phase contrast microscopy—>80% dysmorphic RBCs indicates glomerular bleeding 1, 2, 3
• Look for red blood cell casts, which are pathognomonic for glomerular disease 1, 2
• Lower urinary tract bleeding is associated with >80% normal (non-dysmorphic) red blood cells 1

Associated Findings

• Check for significant proteinuria (>500 mg/24 hours or protein-to-creatinine ratio >0.5), which strongly suggests renal parenchymal disease 1, 2
• Measure serum creatinine to assess renal function—elevated creatinine suggests glomerular disease 1, 2, 4

Critical Pitfalls to Avoid

• Never ignore gross hematuria, even if self-limited—it carries a 30-40% risk of malignancy and requires urgent urologic referral 1, 2, 5
• Do not attribute hematuria to anticoagulation or antiplatelet therapy—these medications may unmask underlying pathology but do not cause hematuria themselves, and full evaluation must proceed regardless 1, 2
• Do not delay evaluation for suspected urinary tract infection without obtaining urine culture first—if culture is positive, treat appropriately and repeat urinalysis 6 weeks after treatment completion to confirm resolution 1, 2, 4
• Exclude menstrual contamination in women by repeating urinalysis 48 hours after cessation of menses 1, 2, 4

When to Suspect Contamination or False Positives

• Menstruation can cause contamination of urine samples in women, leading to false-positive results 1
• Vigorous exercise can cause transient hematuria that resolves with rest—repeat urinalysis 48 hours after cessation of exercise 1, 2
• Dipstick can detect myoglobin (from rhabdomyolysis) or hemoglobin (from hemolysis) without actual intact RBCs present—microscopic examination will show no RBCs in these cases 1