What is the primary function of haptoglobin?

What is the primary function of haptoglobin?

• A. Binds free hemoglobin after RBC lysis to be destroyed by the spleen
• B. Binds iron to transferrin
• C. Converts bilirubin to biliverdin
• D. Acts as an antioxidant in plasma

Answer: (A)

Haptoglobin’s main role is to scavenge free hemoglobin released into the plasma after red blood cell lysis. When intravascular hemolysis occurs, hemoglobin spills into the bloodstream and can cause kidney damage and oxidative injury if left free. Haptoglobin binds this free hemoglobin to form a large Hp–Hb complex that cannot pass through the glomerulus, and this complex is then cleared by the reticuloendothelial system (primarily liver and spleen) via receptors like CD163. This prevents iron loss through the urine and protects tissues from oxidative damage. Transferrin’s job is binding iron in circulation, not haptoglobin. The conversion of bilirubin to biliverdin is mediated by heme oxygenase (and biliverdin reductase), not haptoglobin. While the Hp–Hb complex does help limit oxidative stress, the defining function here is binding free Hb and promoting its clearance, making that choice the best fit.

Haptoglobin’s main role is to scavenge free hemoglobin released into the plasma after red blood cell lysis. When intravascular hemolysis occurs, hemoglobin spills into the bloodstream and can cause kidney damage and oxidative injury if left free. Haptoglobin binds this free hemoglobin to form a large Hp–Hb complex that cannot pass through the glomerulus, and this complex is then cleared by the reticuloendothelial system (primarily liver and spleen) via receptors like CD163. This prevents iron loss through the urine and protects tissues from oxidative damage.

Transferrin’s job is binding iron in circulation, not haptoglobin. The conversion of bilirubin to biliverdin is mediated by heme oxygenase (and biliverdin reductase), not haptoglobin. While the Hp–Hb complex does help limit oxidative stress, the defining function here is binding free Hb and promoting its clearance, making that choice the best fit.