Measurement of the amount of haptoglobin in a specified sample of plasma, the fibrinogen-containing fluid portion of the blood in which the particulate components are suspended. Haptoglobin is a serum alpha2 globulin glycoprotein, produced by the liver, that functions to bind free plasma hemoglobin, which allows degradative enzymes to gain access to the hemoglobin, while at the same time preventing loss of iron through the kidneys and protecting the kidneys from damage by hemoglobin.