What if a urinalysis (UA) shows occult blood but no red blood cells (RBC)?

Occult Blood on Dipstick Without RBCs on Microscopy

A positive dipstick for blood with no RBCs on microscopy is NOT true hematuria and does not warrant urologic evaluation unless microscopy confirms ≥3 RBCs per high-power field. 1

Confirm True Hematuria First

• The American College of Physicians explicitly states that heme-positive dipstick results must be confirmed with microscopic urinalysis demonstrating ≥3 erythrocytes per high-powered field before initiating any further evaluation in asymptomatic adults. 1

• A positive dipstick alone has limited specificity (65-99%) and requires microscopic confirmation before proceeding. 2

• If microscopy shows 0 RBCs, this is a false-positive dipstick result, not hematuria. 1

Common Causes of False-Positive Dipstick

The dipstick detects heme/peroxidase activity, which can be positive without actual RBCs present due to:

• Myoglobinuria from rhabdomyolysis - The classic teaching is that positive dipstick with negative microscopy indicates myoglobin, though this finding has only 41% sensitivity for rhabdomyolysis (55% in severe cases with CPK ≥10,000). 3

• Hemoglobinuria from intravascular hemolysis - Free hemoglobin in urine without intact RBCs. 3

• Contamination - Menstrual blood, vaginal bleeding, or specimen contamination can cause false positives. 1

• Technical factors - Oxidizing contaminants or bacterial peroxidases may trigger the dipstick reaction. 4

Clinical Action Plan

If dipstick shows blood but microscopy shows 0 RBCs:

• Do NOT pursue urologic evaluation - This does not meet criteria for hematuria requiring cancer workup. 1

• Assess for myoglobinuria - Check creatine kinase (CPK), look for muscle injury, dark urine, or renal insufficiency suggesting rhabdomyolysis. 3

• Assess for hemoglobinuria - Check for signs of hemolysis (anemia, elevated LDH, low haptoglobin, jaundice). 3

• Consider specimen issues - In women, ensure clean-catch specimen or consider catheterized sample to exclude vaginal contamination. 1

• Repeat urinalysis - If no clear cause identified, repeat with fresh properly collected specimen to confirm the finding. 1

Critical Pitfall to Avoid

Do not refer to urology or order imaging (CT urography, cystoscopy) based on dipstick alone without microscopic confirmation of RBCs. The entire framework of hematuria evaluation in guidelines is predicated on microscopically confirmed RBCs, not just a positive dipstick. 1 Proceeding with unnecessary urologic workup exposes patients to radiation, invasive procedures, and costs without benefit when true hematuria has not been established. 1

When Microscopy Shows 1-2 RBCs per HPF

• This falls below the threshold of ≥3 RBCs/HPF required to trigger hematuria evaluation. 1

• No urologic workup is indicated at this level. 1

• Consider repeating if clinical suspicion remains high, but isolated findings of 1-2 RBCs are generally not pursued. 1