Which finding helps differentiate hematuria from hemoglobinuria?

• A. Presence of dysmorphic RBCs
• B. Absence of intact red blood cells with dipstick positive for blood
• C. Proteinuria
• D. Pyuria

Answer: (B)

The key idea is that the dipstick for blood detects heme, not intact red blood cells. In hematuria, red cells are present in the urine and you’ll see them on microscopic examination; the dipstick is positive for blood because it’s detecting the red cells’ heme, and you would actually observe red cells in the sediment (often dysmorphic if the source is glomerular). In hemoglobinuria, the red cells have been destroyed, so there are few or no intact red cells on microscopy, yet the dipstick remains positive for blood due to free hemoglobin in the urine. This combination—absence of intact red blood cells on microscopy with a positive dipstick for blood—best differentiates hemoglobinuria from hematuria.