An acid glycoprotein found in blood plasma which, when it binds to free hemoglobin in the blood (i.e. not within a red blood cell), cannot be filtered and eliminated from the body by the kidneys. People with hemolytic disorders (diseases that involve the destruction of red blood cells) have low serum levels of haptoglobin (the normal range is 0.5 - 3.2 g/L).

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.