Clinical Information

Haptoglobin is an immunoglobulin-like plasma protein that binds hemoglobin. The haptoglobin-hemoglobin complex is removed from plasma by macrophages and the hemoglobin is catabolized. When the hemoglobin-binding capacity of haptoglobin is exceeded, hemoglobin passes through the renal glomeruli, resulting in hemoglobinuria.

Haptoglobin has lower serum concentrations in children and therefore is not suited for hemolysis testing. Haptoglobin is an acute-phase reactant, which can develop very high serum levels during periods of inflammation or tissue necrosis. Chronic intravascular hemolysis causes persistently low haptoglobin concentration. Regular strenuous exercise may cause sustained low haptoglobin, presumably from low-grade hemolysis. Low serum haptoglobin may also be due to severe liver disease.

Neonatal plasma or serum specimens usually do not contain measurable haptoglobin; adult levels are achieved by 6 months.

Increase in plasma haptoglobin concentration occurs as an acute-phase reaction. Levels may appear to be increased in conditions such as burns and nephrotic syndrome. An acute-phase response may be confirmed and monitored by assay of other acute-phase reactants, such as alpha-1-antitrypsin and C-reactive protein.