Apolipoprotein H (Apo H), previously known as β2-glycoprotein I, is a multifunctional apolipoprotein that in humans is encoded by the APOH gene. It is a glycoprotein synthesized by liver cells. One of its functions is to bind cardiolipin. Apo H binds to various kinds of negatively charged substances such as heparin, phospholipids, and dextran sulfate. Apo H has a complex involvement in agglutination, it appears to alter ADP mediated agglutination of platelets. It may prevent activation of the intrinsic blood coagulation cascade by binding to phospholipids on the surface of damaged cells. Normally Apo H assumes an anti-coagulation activity in serum (by inhibiting coagulation factors). Its plasma concentrations are strongly associated to metabolic syndrome alterations and vascular disease in type 2 diabetic and could be considered as a clinical marker of cardiovascular risk.