Alpha-2 macroglobulin (A2M) is a tetrameric glycoprotein with a molecular weight of 725 kDa. It is synthesized in the liver and has the role of a serine proteases inhibitor. It inhibits coagulation by inactivating thrombin and kallikrein; it inhibits fibrinolysis by inactivating plasmin and it is also involved in insulin transport. A2M is the principal defensin binding protein. Raised levels of A2M are found in cirrhosis, pregnancy and diabetes.