This is a heterogenous complex of prolactin and immunoglobulin and is the cause of apparent hyperprolactaemia in about 20% of cases.9 Macroprolactin is detected and contributes to total prolactin measured by most commercial immunoassays, and its presence should be considered in all cases of mild to moderate hyperprolactinaemia. This evidence concerns the gene PRL and hyperpituitarism.