American Board of Internal Medicine (ABIM) Certification Practice Exam

What characterizes hemoglobinuria compared to true hematuria?

1. The absence of erythrocytes on urine microscopy

2. Presence of grossly visible blood

3. Higher levels of protein in urine

4. Lower urine pH

The correct answer is: The absence of erythrocytes on urine microscopy

Hemoglobinuria is characterized by the presence of hemoglobin in the urine, which occurs when hemoglobin is released into the bloodstream and subsequently filtered by the kidneys. This condition is distinct from hematuria, which involves the presence of intact red blood cells (erythrocytes) in the urine. The critical feature that separates hemoglobinuria from true hematuria is the absence of erythrocytes on urine microscopy. In hemoglobinuria, the urine may appear dark or red due to the presence of free hemoglobin, but when examined microscopically, there are no red blood cells present. This is in contrast to hematuria, where the presence of erythrocytes would be evident upon microscopic examination, indicating that the blood is coming directly from the urinary tract. The other options do not accurately distinguish hemoglobinuria from hematuria. While both conditions can lead to the appearance of blood in the urine, the presence of visible blood does not specifically indicate hemoglobinuria as it could also be seen in hematuria. The levels of protein in the urine or urine pH do not serve as defining factors between these two conditions either, as they can vary independently based on multiple other factors unrelated to the presence of hemoglobin