Causes of Pseudohematuria
Pseudohematuria refers to red or discolored urine that mimics hematuria but does not contain actual red blood cells. It is an important differential diagnosis when evaluating patients with apparent blood in the urine 1, 2.
Common Causes of Pseudohematuria
Food and Dietary Sources
- Beetroot consumption
- Foods with red or purple pigments
- Blackberries
- Rhubarb
Medications
- Mesalazine (can react with toilet bowl cleaners containing bleach) 3
- Rifampin
- Phenazopyridine
- Doxorubicin
- Phenolphthalein (in laxatives)
- Nonsteroidal anti-inflammatory drugs (NSAIDs) 4
Metabolic Conditions
- Porphyria
- Hemoglobinuria (from intravascular hemolysis) 5
- Myoglobinuria (from rhabdomyolysis)
Chemical Reactions
- Reaction between medications and toilet bowl cleaners 3
- Highly alkaline urine
Distinguishing Pseudohematuria from True Hematuria
Key Diagnostic Tests
- Urinalysis with microscopy: Absence of RBCs despite positive dipstick for blood suggests pseudohematuria 2
- Urine dipstick test patterns:
Finding True Hematuria Hemoglobinuria Myoglobinuria Other Pigments Dipstick Positive Positive Positive Negative RBCs on microscopy Present Absent Absent Absent Plasma color Normal Pink/red Normal Normal Urine sediment Red Clear red Clear red/brown Varies
Clinical Approach to Suspected Pseudohematuria
Detailed medication history
- Focus on medications known to cause urine discoloration
- Ask specifically about NSAIDs, which have been implicated in up to 54% of cases of idiopathic hematuria 4
Dietary history
- Recent consumption of foods with strong pigments
Laboratory evaluation
- Complete urinalysis with microscopy (to confirm absence of RBCs)
- Urine culture (to rule out infection)
- If hemoglobinuria is suspected: serum haptoglobin, LDH, and peripheral blood smear
Consider specialized testing for specific conditions
- Flow cytometry for paroxysmal nocturnal hemoglobinuria if hemoglobinuria is present 5
- Urine porphobilinogen for porphyria
Important Clinical Considerations
- Pseudohematuria must be distinguished from true hematuria, as the latter requires thorough evaluation for potentially serious conditions including malignancy 6, 7
- The American Urological Association recommends that patients with true microscopic hematuria (>3 RBC/HPF) undergo risk stratification and appropriate evaluation 1, 6
- Hemoglobinuria is often misdiagnosed as hematuria, leading to unnecessary urologic workup 5
- In patients taking mesalazine for inflammatory bowel disease, be aware that a chemical reaction with toilet bowl cleaners can cause alarming urine discoloration 3
Pitfalls to Avoid
- Assuming all red urine contains blood without microscopic confirmation
- Failing to take a thorough medication and dietary history
- Overlooking hemoglobinuria as a cause of red urine in patients with hemolytic conditions
- Missing the distinction between glomerular and non-glomerular sources of true hematuria when it is present
- Conducting extensive urologic workups before ruling out pseudohematuria
By systematically evaluating patients with discolored urine and confirming the presence or absence of actual red blood cells, clinicians can avoid unnecessary testing while ensuring appropriate management for patients with true hematuria.