The function of this protein is to bind free hemoglobin to prevent the loss of hemoglobin and its constituent iron into the urine:

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Binding free hemoglobin in plasma to prevent its loss in urine is the role of haptoglobin. When red cells are destroyed in the bloodstream, hemoglobin is released and can be filtered by the kidneys, potentially causing iron loss and oxidative damage. Haptoglobin binds free hemoglobin with high affinity, forming a complex too large to be filtered, so iron is conserved and hemoglobin is removed safely by macrophages via the CD163 pathway. Its levels drop during active intravascular hemolysis because the haptoglobin-hemoglobin complex is cleared. The other proteins have different tasks: alpha2-macroglobulin inhibits proteases, beta2-microglobulin is part of MHC class I and a kidney function marker, and ceruloplasmin is a copper-containing enzyme involved in iron metabolism but not Hb scavenging.