Hemoglobinuria is defined as the presence of hemoglobin in the urine and it is usually noted as a positive (+) result in the urinalysis section.
Hemoglobin is a protein of the red blood cells (RBCs) that carries oxygen from blood to organs and tissues. Hemoglobin may be present in the urine as a result of red blood cell lysis that occurs in the urinary tract, particularly in dilute, alkaline urine.
However, the most common cause is due to intravascular lysis, which is the breakdown of red blood cells within the vessels. When there is an elevated concentration of hemoglobin in the blood (for example, in case of suffering hemolytic anemia) and the amount of free hemoglobin present exceeds the haptoglobin content, the hemoglobin will be filtered in the kidneys and excreted into the urine.
Urine with hemoglobin usually has a red or brown-red transparent color.
This test is performed to detect intravascular lysis, an excessive destruction of red blood cells (RBCs) in the bloodstream due to hemolytic anemia, transfusion reactions or spider or snake bites.
This test is performed along with other urine tests. The patient must collect a sample of the urine in a specific container using a special kit. This sample will be sent to the lab for the analysis.
It is necessary to avoid specimen contamination with menstrual blood or trauma caused by catheter insertion.
Hemoglobin in urine can be tested either with a dipstick or with a tablet that change of color in the presence of hemoglobin in the urine.
In laboratories, there are automated machines that perform the analysis, but it is also possible to buy strips that let you analyze a urine sample at home. They comprise up to 10 or more different reagents or chemical pads to perform different urine tests at the same time.
The urine hemoglobin test must be negative to be considered within normality.
A positive result of hemoglobin in the urine (hemoglobin in urine +) may be a sign of:
There are three reasons that a urine sample may show a positive result for blood in a dipstick:
It is important to discern between hematuria (blood in your urine), which is the presence of intact red blood cells in the urine, from hemoglobinuria, which is the presence of hemoglobin without the presence of intact red blood cells. The dipsticks cannot discern between hematuria, hemoglobinuria or myoglobinuria.
Therefore, in case of a positive result, it is necessary a microscopic examination of the urine sample to detect red blood cells in the urine sediment.
If the dipstick is positive and there are no red blood cells in the urine sediment under the microscope is a sign of hemoglobinuria or myoglobinuria. Many testing methods may differentiate a positive urine blood result due to hemoglobin from one that is due to myoglobin.