What Does Trace Blood in Urinalysis (±) Mean?
When a routine urine test shows trace blood, also referred to as hemoglobinuria, it indicates the possible presence of blood in the urine—even if not visible to the naked eye. A result marked as (±) for occult blood suggests a borderline or minimal detection, meaning there might be microscopic hematuria. This is considered a preliminary sign and requires further investigation to determine whether true hematuria exists.
Understanding the Significance of (±) Blood in Urine
The (±) symbol in urinalysis reflects a faint positive reaction—essentially hovering between negative and positive. In clinical terms, this means that while blood components such as hemoglobin have been detected in the urine, the levels are very low. However, this doesn't automatically confirm the presence of intact red blood cells in the urinary tract.
Differentiating Between Hematuria and Hemoglobinuria
To accurately interpret these results, healthcare providers typically recommend a urine sediment microscopy. This test examines whether actual red blood cells are present and elevated in the urine. If the microscopic analysis reveals an increased number of red blood cells, then the (±) reading likely indicates true hematuria—possibly stemming from conditions affecting the kidneys, ureters, bladder, or urethra.
Conversely, if the dipstick test shows a positive or trace (±) result for blood but the urine sediment shows no red blood cells, this discrepancy may point to hemoglobinuria rather than hematuria. Hemoglobinuria occurs when red blood cells break down within the bloodstream, releasing free hemoglobin into the urine—a hallmark of intravascular hemolysis.
Potential Underlying Causes of False-Positive Results
In cases where blood is detected on the test strip but no red blood cells appear under the microscope, clinicians often explore non-urinary sources. Conditions such as autoimmune hemolytic anemia, paroxysmal nocturnal hemoglobinuria (PNH), transfusion reactions, or other hemolytic disorders could be responsible. Additional blood tests—including serum haptoglobin, lactate dehydrogenase (LDH), reticulocyte count, and direct Coombs test—are usually necessary to evaluate for hemolysis.
Next Steps After a (±) Blood Finding
A trace blood result shouldn't be ignored, nor should it cause immediate alarm. It serves as a signal for further evaluation. Depending on the patient's medical history, symptoms (such as pain, fatigue, or dark-colored urine), and additional lab findings, doctors may order imaging studies like ultrasound or CT scans, or refer the patient to a nephrologist or urologist.
In asymptomatic individuals with isolated (±) results and normal sediment, repeat testing is often recommended after hydration and avoiding potential confounders like intense exercise or menstruation. Persistent abnormalities warrant deeper investigation to rule out chronic kidney disease, glomerulonephritis, urinary tract infections, or even malignancies.
In summary, a (±) blood result in a standard urinalysis is a subtle but important clue—not a diagnosis. Proper interpretation hinges on correlating chemical strip data with microscopic examination and clinical context. Early follow-up ensures timely identification of both benign variations and serious underlying conditions.