A 24-year-old man is noted to have urine analysis that is positive for blood. The microscopic examination of the urine is negative for casts or red blood cells. Which of the following is the most likely diagnosis

A urinalysis that is positive for blood does not distinguish between myoglobin and hemoglobin. A microscopic urine exam is necessary for a definitive diagnosis. In a patient with myoglobinuria, a microscopic evaluation will fail to show the presence of red blood cell (RBC) casts or intact RBCs. Gross myoglobinuria can lead to an abnormal coloration of the urine and is typically described as "cola colored." Hematuria and renal cell carcinoma would be expected to produce urine analysis and microscopic exam that are positive for RBCs, whereas nephritic syndrome would be expected to have RBC casts.