The easiest way to differentiate between blood in the urine and myoglobinuria is to spin down the sample.
Will get a pellet of red cells with normally colored urine if hematuria; urine will remain discolored if myoglobinuria/hemoglobinuria.
Urine dipstick does NOT differentiate between the 3 main causes of red urine – hematuria, hemoglobinuria, and myoglobinuria.
To differentiate between hematuria and hemoglobinuria, spin down a plasma sample.
Plasma will remain pink if hemolysis present (causing hemoglobinuria).
Complete blood count and serum biochemistry analysis can also help differentiate.
Will see increase in muscle enzymes (creatine kinase, aspartate aminotransferase) with myoglobinuria.
May see increase in bilirubin with certain types of hemolysis.
May see anemia with changes to the MCH/MCHC and hemolysis or urinary tract hemorrhage depending on severity and duration.
Lastly, microscopic exam of urine sediment can also be used to identify red blood cells.
Ref: Bassert, Beal and Samples, McCurnin’s Clinical Textbook for Veterinary Technicians, 9thed, pp. 398-404. Image courtesy of James Heilman, MD.
