Haptoglobin

Haptoglobin is a protein produced by the liver that binds to the free haemoglobin released by red blood cells. This binding prevents haemoglobin from causing oxidative damage and facilitates its elimination from the bloodstream.

Haptoglobin levels fall significantly in the presence of intravascular haemolysis because the protein binds to the free haemoglobin in lysed red blood cells, and the complex is then rapidly eliminated from the circulation. A low haptoglobin level in the context of anaemia suggests that haemolysis is the cause.

In contrast, haptoglobin levels are generally normal in non-haemolytic anaemias, such as those caused by blood loss or reduced RBC production. Haptoglobin is, therefore a useful marker for differentiating haemolytic anaemia from other types of anaemia.

In neonates, particularly those with blood group incompatibilities (e.g. Rh or ABO incompatibility), haptoglobin levels can be used to assess the extent of haemolysis. A low haptoglobin level associated with a high bilirubin level and anaemia may indicate significant haemolysis, warranting prompt intervention.

Haptoglobin is produced by the liver and levels may fall in liver diseases, such as cirrhosis or hepatitis, due to deficient synthesis. In this case, the low level of haptoglobin reflects the reduced capacity of the liver to produce the protein rather than haemolysis.

Haptoglobin is an acute-phase protein, which means that its levels can rise in response to inflammation, infection or tissue damage. Elevated levels of haptoglobin can be observed in inflammatory and autoimmune conditions, although it is not a specific marker of these diseases.