Biological or Clinical Significance:
HDL cholesterol (HDL-C) is a powerful inverse predictor of risk of coronary heart disease (CHD). Guidelines published by the American Heart Association (AHA) and the National Cholesterol Education Program (NCEP), which is sponsored by the National Heart, Lung and Blood Institute (NHLBI), recommend that physicians determine HDL-C levels together with other tests in a standard lipid profile prior to administering dietary or drug therapies for CHD. The NCEP guidelines state that patients with high cholesterol or borderline high cholesterol with risk factors (e.g. HDL-C less than 40 mg/dL, hypertension, smoking, family history, etc.) be tested for HDL-C. Subsequently, HDL-C and other lipid parameters should be measured 3-4 times per year to monitor the progress of therapy. Because of its protective effect, the NCEP has designated high HDL-C at or above 60 mg/dL as a negative risk factor.
Principle of Test Method:
Serum HDL-C and other HDL components are traditionally assayed by precipitation of apolipoprotein B containing lipoproteins (VLDL, LDL and IDL) and measurement of the HDL components in the supernate. HDL is a heterogeneous group of molecular aggregates. It contains apolipoproteins A-I, A-II and A-IV, as well as phospholipids, triglyceride, and cholesterol. A portion of the HDL particles also contains apolipoprotein E. This fraction of HDL is difficult to recover by traditional precipitation techniques, such as dextran sulfate-Mg, heparin-Mg, and phosphotungstate. However, precipitation of serum or serum fractions with polyethylene glycol (PEG), recovers a larger proportion of the apolipoprotein E-rich HDL. PEG is a synthetic polymer that is manufactured in a wide range of different molecular weights. The PEG used in this protocol has been shown to recover a large fraction of the apolipoprotein E-rich HDL. This occurs with essentially complete precipitation of apolipoprotein B containing lipoproteins. The resulting HDL supernate is then determined for cholesterol, by an enzymatic procedure.