Regional Laboratory
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Research advances over the last decade have revealed new relationships between lipid risk factors and cardiovascular disease. The power of laboratory testing to detect patients at high risk for coronary disease is greater than ever. This month’s algorithm, “Guidelines for Assessing Risk of Coronary Heart Disease and Lipid Testing” is intended to assist physicians in choosing the best tests for patients in various risk categories so that therapies may be properly applied to reduce the risk for future coronary heart disease.
The guidelines are taken from the NIH National Cholesterol Education Program’s Adult Treatment Panel II (1993). They represent a consensus of the best science available at that time, and the data which has accumulated since then has largely endorsed the guidelines.
The patient evaluation process begins by determining if clinically-evident vascular disease (a history of MI, CABG, PTCA, angina, peripheral vascular disease, or stroke) is present. If Yes, then the Secondary Prevention algorithm (page 3) is recommended; if No, the Primary Prevention approach should be followed (page 2). If Primary Prevention is needed, the level of risk is determined by a combination of serum lipid and lipoprotein levels AND the presence/absence of a variety of non-lipid risk factors (page 1). Note particularly that while a low HDL-C (<35 mg/dL) is an adverse risk factor, a high HDL-C (>60 mg/dL) is a beneficial risk factor which can “cancel” one adverse factor. The algorithms on pages 2 and 3 ultimately require a measured LDL-C for accurate CHD risk assessment for most patients with a cholesterol over 200 mg/dL or with an HDL-C of less than 35 mg/dL.
Systematic use of the NCEP guidelines will help identify patients at increased risk for CHD. Other issues such as the role of triglycerides, Lp(a), remnant lipoproteins, homocysteine and oxidized LDL in CHD risk prediction are less well-defined and currently being investigated.
Atherogenic Dyslipidemia
Evaluating a patient’s risk for coronary artery disease (CAD) is getting easier. In the past, it has been difficult, not only for the practitioner but also for the “experts,” to weigh the various contributions that total, LDL and HDL cholesterol, and triglycerides made to the overall risk profile. The first NCEP Adult Treatment Panel (ATP) guidelines (1988) focused on LDL cholesterol; NCEP ATP II (1993) elevated the importance of HDL cholesterol and recognized the marked increase in risk for cardiovascular events associated with the presence of documented CAD. Many practitioners have long appreciated that a significant proportion of CAD patients do not have marked LDL cholesterol elevations; instead, they have several risk factors which include mild LDL and triglyceride elevations, moderate HDL reductions, central obesity, mild hypertension and insulin resistance. This constellation has been called clustered risk factors, Reaven’s syndrome, the deadly quartet, syndrome X, the metabolic syndrome, or the insulin resistance syndrome.
In an effort to draw attention to the lipid profile characteristic of this common syndrome, Scott Grundy, a leading lipidologist, has coined the term “Atherogenic Dyslipidemia” (ADL). The parameters for ADL are as follows:
· LDL-cholesterol > 130 mg/dL
· Triglycerides > 150 mg/dL
· HDL-cholesterol < 40 mg/dL for men & < 50 mg/dL for women
Patients with this profile also are very likely to have “small, dense LDL particles” sometimes called LDL “pattern B,” and increased levels of apolipoprotein B-100.
The cutpoints listed above are not currently considered abnormal (except for LDL-C), and are actually typical for middle-age, white males in the US today. Thus, such findings are often dismissed as normal and the attendant risk ignored. The prevalance of the complete syndrome (all three abnormalities appearing in the same individual) is probably equal to that of isolated hypercholesterolemia (i.e., LDL-C > 160 mg/dL) which is 25-30% of the adult population.