From the Guidelines
A trace amount of hemoglobin in urinalysis indicates a small presence of blood in the urine, which warrants further investigation but is not necessarily an emergency. This finding suggests possible bleeding somewhere in the urinary tract, hemolysis (breakdown of red blood cells), or myoglobin release from muscle damage. Common causes include urinary tract infections, kidney stones, glomerulonephritis, trauma, strenuous exercise, menstruation in women, or certain medications.
Evaluation and Management
To evaluate this finding, additional tests are typically needed, including:
- Microscopic examination of the urine sediment to check for red blood cells
- Protein measurement
- Possibly imaging studies of the urinary tract According to the American Urological Association, the recommended definition of microscopic hematuria is three or more red blood cells per high-power field on microscopic evaluation of urinary sediment from two of three properly collected urinalysis specimens 1.
Patient Advice
Patients with trace hemoglobinuria should:
- Increase fluid intake to help flush the urinary system
- Follow up with their healthcare provider for further assessment If accompanied by symptoms like pain, fever, or changes in urination patterns, medical attention should be sought sooner. The presence of hemoglobin is detected through chemical reagent strips that react with the peroxidase-like activity of hemoglobin, causing a color change on the dipstick proportional to the amount present.
Clinical Considerations
It is essential to consider risk factors for significant disease, such as age, sex, and medical history, when evaluating patients with trace hemoglobinuria 1. A threshold of at least 3 erythrocytes per high-powered field is considered abnormal across several recommendations 1.
From the Research
Trace Hemoglobin in Urinalysis
- Trace hemoglobin in urinalysis can be detected using urine dipstick testing, which may suggest the presence of blood 2
- However, results should be confirmed with a microscopic examination to differentiate between hematuria, hemoglobinuria, and myoglobinuria 2
- Myoglobin reacts positively for blood by urine dipstick, which can serve as an indicator of myoglobinuria, but may also be confused with hemoglobinuria 3
- Urinalysis results can reliably predict the absence of myoglobinuria and could be used to avert overtesting for urine myoglobin while also providing useful diagnostic information when urine myoglobin test results are not immediately available 3
- Hemoglobinuria can be misidentified as hematuria, and specific characteristics in a dipstick test or urinalysis can guide differentiation of these two causes of discolored urine 4
- Pigmenturia, caused by the presence of dyes, urinary metabolites, and certain drugs in the urine, can be easily confused with hematuria, and the peroxidase activity can be positively affected by the presence of non-Hb peroxidases 5
Differentiation of Hemoglobinuria and Hematuria
- Differentiating myoglobinuria from hemoglobinuria is important, as clinicians' concern over myoglobinuria is to protect the patient from acute renal disease 6
- Hemoglobinuria manifesting as discolored urine can be easily confused with other common causes of discolored urine, including hematuria and myoglobinuria 4
- The implementation of expert systems may be helpful in detecting preanalytical and analytical errors in the assessment of hematuria, and correcting for dilution using osmolality, density, or conductivity may be useful for heavily concentrated or diluted urine samples 5