Apolipoprotein A

Apolipoprotein A (Apo A) is the main protein in the HDL cholesterol particle (good cholesterol). Apo A enables HDL to take on cholesterol, which is then eliminated from the intestine via the liver's conversion to bile acid. This is the only means of eliminating cholesterol from the body. Apo A levels are expressed in grams per liter (g/L), and the reference values are slightly higher in women (1.25 to 2.15 g/L) than in men (1.10 to 2.05 g/L).

In general, levels of Apo A reflect levels of HDL cholesterol. The higher your HDL or Apo A, the better your protection from cardiovascular disease. However, there are different types of Apo A (Apo A-I, Apo A-II) and the protective effect of HDL may vary depending on the proportions of each subtype. An increase in Apo A-I is more closely associated with a reduction in the risk of a first heart attack or better statin protection than an increase in HDL cholesterol. Even when normal HDL levels are present, low Apo A-I levels better predict the presence of preclinical atherosclerosis (the onset of artery obstruction by cholesterol plaques).