Haptoglobin, serum

Haptoglobin is a plasma glycoprotein synthesized in the liver whose primary function is to irreversibly bind free oxyhemoglobin and deliver it to the reticuloendothelial system. The resulting hemoglobin-haptoglobin complex binds to the CD163 receptor on macrophages, is internalized, and degraded by lysosomes to amino acids and iron.  Haptoglobin prevents loss of hemoglobin into urine and conserves iron.

When the hemoglobin-binding capacity of haptoglobin is exceeded, hemoglobin is excreted by the kidneys, resulting in hemoglobinuria. 

Haptoglobin is an acute phase protein and plasma levels are increased in patients with acute and chronic inflammatory disorders and malignancies.  Decreased levels are associated with hemolysis, liver disease, sickle cell anemia, and genetic haptoglobinemia. 

Neonates do not have measurable quantities of haptoglobin, but adult levels are reached by 6 months of age. 

Clinically, haptoglobin levels are useful in the work-up of patients with suspected intravascular hemolysis. Typically, haptoglobin levels fall below 30 mg/dL following hemolysis. However, haptoglobin levels need to be interpreted carefully.  Often, haptoglobin levels are not drawn until after a patient has been transfused with red blood cells. Units of stored blood contain sufficient amounts of free hemoglobin to decrease haptoglobin. Ideally, haptoglobin levels should be ordered prior to transfusion.

Reference range is 30 - 200 mg/dL.

Specimen requirement is one SST tube of blood.

Reference

Shih AW, McFarlane A, Verhovsek M. Haptoglobin testing in hemolysis: measurement and interpretation. Am J Hematol. 2014;89(4):443-447. doi:10.1002/ajh.23623