The test for blood on the reagent strip is based on the peroxidase-like activity of hemoglobin, which catalyzes the reaction of heme and the chromogen tetramethylbenzidine.
A urine specimen with hemoglobin (or myoglobin) will produce a uniform green to green-blue color. Intact RBCs will lyse on contact with the reagent pad, producing a speckled pattern.
The test is sensitive to free hemoglobin, myoglobin, and a minimum of 5 intact RBCs per microliter of urine.
