Haptoglobin is an acute phase protein and is part of immune system-mediated defense mechanisms found in the blood various animal species. Under normal conditions, haptoglobin is either absent from the blood or present at very low levels. However, haptoglobin can increase significantly in response to acute infection, inflammation or trauma.

Several functional properties of haptoglobin have been described. The major biological function of haptoglobin is to bind free hemoglobin in an equimolar ratio with very high affinity to prevent hemoglobin-mediated renal parenchymal injury and loss of iron following intravascular hemolysis. The complex of haptoglobin with hemoglobin is metabolized in the hepatic reticuloendothelial system. Biosynthesis of haptoglobin occurs not only in the liver, but also in adipose tissue and lung, providing antioxidant and antimicrobial activity.

Different studies show differences in average measurements of serum haptoglobin according to horse age. In foals, the reference range of haptoglobin is significant higher compared to adult horses. Comparisons within adult horses showed no differences between the different age groups. In equine medical research, haptoglobin is used as one of the major
indexes in addition to fibrinogen and serum amyloid A to examine the acute phase reaction in horses. Haptoglobin has been used to assess postoperative inflammatory reactions. Haptoglobin can be used as a global parameter for inflammatory processes, since it is not disease-specific. This is underlined by several studies examining the haptoglobin serum levels in relation to different diseases such as respiratory and orthopedic disorders or surgical interventions.

Studies have strengthened haptoglobin as an alternative to serum amyloid A or fibrinogen as a diagnostic instrument for an acute phase reaction. In combination with serum amyloid A, haptoglobin can be used to research inflammatory kinetic.

In equine medicine, haptoglobin, as an acute phase protein, is helpful in research of various diseases.