American Board of Internal Medicine (ABIM) Certification Practice Exam

What indicates a positive result for hemoglobinuria in urine testing?

1. Red blood cell presence

2. Prussian blue stain for urine hemosiderin

3. Presence of myoglobin

4. Oxygen saturation levels

The correct answer is: Prussian blue stain for urine hemosiderin

A positive result for hemoglobinuria in urine testing is indicated by the presence of free hemoglobin in the urine, which can be detected through specific urine tests. The correct answer is the Prussian blue stain for urine hemosiderin. This stain indicates the presence of hemosiderin, which is a byproduct of hemoglobin breakdown. When there is hemolysis, hemoglobin is released into the bloodstream, filtered by the kidneys, and appears in the urine. As hemoglobin breaks down further in the urine, it can form hemosiderin. Red blood cells in urine suggest hematuria, which is distinct from hemoglobinuria. It indicates the presence of intact red blood cells rather than free hemoglobin. Myoglobin presence relates to muscle injury and is associated with myoglobinuria, not hemoglobinuria. Oxygen saturation levels pertain to arterial blood gas analysis and oxygen transport but do not directly indicate hemoglobinuria in urine testing. Thus, the detection of hemosiderin using the Prussian blue stain is a specific marker indicating hemoglobin breakdown in the urine.