Cholesterol Levels


Doctors measure apolipoproteins for clues to the risk of coronary heart disease.
Doctors measure apolipoproteins for clues to the risk of coronary heart disease.
Publications International, Ltd.

You may hear about tests that measure apolipoproteins, which are the specific types of proteins that your HDLs and LDLs contain. They are alphabetically designated as A, B, C, D, and E.

LDL contains apolipoprotein B (apo B); HDL contains apolipoprotein A-1 (apo A1). A recent study indicated that, in comparison to the standard blood-cholesterol tests, the ratio of apo B to apo A1 is the best predictor of those at risk of heart attack. For example, some people who have normal levels of LDL may have higher-than-normal levels of apo B (usually there's only one apo B molecule on each LDL), and this higher level may indicate greater risk.

One clue to an increase in the number of apo B particles is an elevated level of triglycerides -- 150 mg/dL or greater. When LDL-cholesterol levels are normal but triglyceride levels are elevated, something called non-HDL cholesterol should be measured.

Non-HDL cholesterol is the total of VLDL and LDL cholesterol, both of which contain apo B particles. As a result, measurement of non-HDL cholesterol provides more accurate information about atherogenic particles.

Finally, a low level of apo A1, the apolipoprotein found on HDL, indicates a greater risk of coronary heart disease. Currently, there doesn't seem to be any clinical advantage to measuring these smaller particles of HDL cholesterol, as this information doesn't affect the course of treatment; in the future, however, if effective medications are developed that target HDL cholesterol, this may change.

Preliminary research also appears to indicate that genetic differences in apo E, a key protein in the metabolism of LDLs, may predict a person's risk for coronary heart disease. For example, people who have one form of apo E appear to have higher LDL levels and develop coronary heart disease earlier than those with other forms. On the other hand, those who have a different form of apo E may have some protection from heart disease.

Researchers have also found a way to measure lipoprotein (a), or Lp(a), a cholesterol-rich lipoprotein that is associated with a tendency toward clotting (thrombosis) and enhanced plaque formation. In some studies, high levels of Lp(a) seem to indicate an increased risk of coronary heart disease in men and women. Estrogen and ­niacin are among the few drugs that are known to lower Lp(a). However, because the research findings relating Lp(a) and coronary heart disease are not consistent, routine measurement and treatment of Lp(a) are not recommended. This measurement may, however, be helpful in individuals with a personal or family history of premature coronary heart disease, indicating additional benefit from a more intensive reduction in LDL cholesterol.

Measurements of apolipoproteins are providing researchers with more and more tools for predicting an individual's risk of coronary heart disease. Some of these tests are becoming available at laboratories. Talk with your doctor to determine if any of these newer tests, in addition to the standard blood-cholesterol tests, would be beneficial in providing more information about your cholesterol levels. Be advised, however, that not all these tests are standardized, they tend to be more expensive, and they may not provide information that would change the course of treatment.

Along with apolipoproteins and overall cholesterol, doctors must check your triglycerides. On the next page, learn what these are and why a high level of triglycerides may be harmful.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.