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Decreased to absent levels occur more with intravascular than extravascular hemolysis: haptoglobin binds hemoglobin, and carries it to the reticuloendothelial system. Thus, haptoglobin is useful in work-up for hemolytic states. It is low in the megaloblastic anemias, which have a hemolytic component. It is decreased in infectious mononucleosis. Decreases can occur with hematoma or tissue hemorrhage. Haptoglobin can be low with liver disease. Congenital absence occurs (small fraction of certain ethnic populations have ahaptoglobinemia, absence of detectable haptoglobin). Frequently elevated as an acute phase reactant, in inflammatory disorders (eg, collagen diseases, infections, tissue destruction, and with advanced malignant neoplasms).1
During inflammation or steroid therapy, normal concentrations do not rule out hemolysis; decreased with oral contraceptives; increased with androgens
Haptoglobin is a protein that binds free hemoglobin. Part of α2 on serum protein electrophoresis, serum haptoglobin is a glycoprotein consisting of two pairs of nonidentical chains, α and β, made by the liver. The subunit structure is represented as α2β2. The haptoglobin-bound hemoglobin complex is removed rapidly by the reticuloendothelial system and metabolized to free amino acids and iron in just a few hours. This represents an efficient method for the conservation of iron. Low α2 is commonly due to hemolysis and/or liver disease. Serum protein electrophoretic pattern showing low albumin, polyclonal increase in γ-globulin, and decrease in α2-globulin shown to be due to decreased haptoglobin has been correlated with poor prognosis in severe liver disease.2 Haptoglobin is decreased for two to three days after only 25 mL of blood is lysed.1 Thus, transfusions, which contain red blood cells which do not all survive in the recipient, can lower the level. The decrease in haptoglobin (after hemolysis) precedes any drop in hemopexin levels or the appearance of methemalbumin in serum or urine. Myoglobin, unlike hemoglobin, is not bound by haptoglobin.
1. Peters T Jr. Proteins. In: Brown SS, Mitchell FL, Young DS, eds. Chemical Diagnosis of Disease. Amsterdam, Holland: Elsevier/North Holland Biomedical Press;1979:311-362.
2. Fitzmaurice M, Valenzuela R, Winkelman EI. Serum protein electrophoresis pattern associated with decrease serum haptoglobin as a poor prognostic indicator in severe liver disease. Am J Clin Pathol. 1989; 91:365. During inflammation or steroid therapy, normal concentrations do not rule out hemolysis; decreased with oral contraceptives; increased with androgens
