Clinical diagnosis of lipid disorders

Atherosclerotic cardiovascular disease is a major health problem in the United States. In particular, coronary heart disease (CHD) is the leading cause of death in men and women in the United States, as well as in other industrialized countries. Extensive observational epidemiologic data within and between populations have strongly linked such various factors as untreated hypertension, diabetes, cigarette smoking, and lipid abnormalities to the development of CHD. With respect to lipoprotein parameters, elevated total and low-density lipoprotein cholesterol (LDL-C) and low levels of high-density lipoprotein cholesterol (HDL-C) have been strongly associated with CHD risk. Emerging evidence suggests that other lipoprotein abnormalities also are associated with premature CHD, including elevated levels of lipoprotein(a), triglyceride-rich lipoproteins such as small very-low-density lipoproteins and intermediate-density lipoproteins, small and dense LDL particles, and the magnitude of postprandial lipemia. Extensive primary and secondary clinical trial evidence has established that favorably altering dyslipidemias through diet and a variety of pharmacologic agents produces clear improvements in CHD end points. The extent of this benefit depends on the presence or absence of clinical atherosclerotic disease, as well as other CHD risk factors, and the severity of one or more lipoprotein abnormalities. CHD patients and individuals with multiple risk factors, but free of clinical CHD, derive the greatest absolute benefit from lipid treatment directed at reducing LDL-C. The dyslipidemias that impart high risk are severely elevated LDL-C (> 200 mg/dL), combined high LDL-C and low HDL-C (< 35 mg/dL), and combined hyperlipidemias (non-HDL-C > 200 mg/dL with low HDL). The purpose of this review is to aid the primary care physician in identifying these important dyslipidemias and to critically analyze the relative importance of various lipoproteins on atherosclerotic risk.