In hemolytic anemia, hemoglobinuria occurs when

In hemolytic anemia, hemoglobinuria occurs when

• A. Haptoglobin is depleted
• B. Hemopexin is depleted
• C. Hemoglobin is oxidized
• D. Erythropoietin is decreased

Answer: (A)

When hemolysis occurs inside blood vessels, red blood cells release hemoglobin directly into the plasma. Haptoglobin binds this free hemoglobin to form a complex that the liver clears, preventing the loss of hemoglobin in urine and protecting the kidneys from heme toxicity. If the destruction is heavy, haptoglobin gets used up and becomes depleted. Once there’s no more haptoglobin to bind the circulating Hb, free hemoglobin can be filtered by the kidneys and show up in urine as hemoglobinuria. The other ideas don’t fit this pathway: hemopexin binds free heme rather than hemoglobin, Hb oxidation to methemoglobin isn’t the trigger for Hb in urine, and decreased erythropoietin reflects reduced production rather than increased destruction.

When hemolysis occurs inside blood vessels, red blood cells release hemoglobin directly into the plasma. Haptoglobin binds this free hemoglobin to form a complex that the liver clears, preventing the loss of hemoglobin in urine and protecting the kidneys from heme toxicity. If the destruction is heavy, haptoglobin gets used up and becomes depleted. Once there’s no more haptoglobin to bind the circulating Hb, free hemoglobin can be filtered by the kidneys and show up in urine as hemoglobinuria. The other ideas don’t fit this pathway: hemopexin binds free heme rather than hemoglobin, Hb oxidation to methemoglobin isn’t the trigger for Hb in urine, and decreased erythropoietin reflects reduced production rather than increased destruction.