Apolipoprotein A is a type of apolipoprotein, which is the protein part of a lipoprotein. There are various types of apolipoproteins, including Apo A, Apo B, Apo C, etc. Among them, Apo A is the main structural protein that constitutes HDL in human body, because Apo A can effectively remove lipids from tissues and has the effect of fighting against atherosclerosis. Therefore, in clinical practice, the concentration of ApoA can be measured to make an early assessment of the susceptibility to coronary heart disease and atherosclerosis. With a high ApoA concentration, the patient is significantly less likely to develop coronary heart disease. If ApoA concentration is decreased, it is seen in familial ApoA deficiency. In addition, when there is acute myocardial infarction, diabetes mellitus, or chronic liver disease, ApoA concentrations may also be significantly reduced.