The association between plasma levels of cholesterol and coronary artery disease has been well established. Most work has focused on the direct relationship between low density lipoprotein (LDL) cholesterol and risk of a cardiac event, as LDL is the major carrier of plasma cholesterol. LDL particles are formed with a cholesterol ester-rich core surrounded by phospholipid, free cholesterol, and an apolipoprotein, apo B-100. An antigen, Lp(a) confers heterogenicity to LDL. Lp(a) is similar in structure to LDL. It is felt that Lp(a) may be the most atherogenic of the lipoproteins on a per mole basis. To interpret elevated Lp(a), knowledge of Lp(a) intra-individual and biological variation is required. However, conflicting estimates of variation range from 2.8-16.6% using different analytical methods and subjects with a wide range of Lp(a) levels.