ApoB, Cholesterol Testing And Predicting Cardiovascular Disease

A statement by the American College of Cardiology and the American Diabetes Association suggests that ApoB levels should be measured in addition to LDL cholesterol (the "bad" cholesterol) to assess cardiovascular risk in some patients. ApoB is a protein that is associated with LDL particles that may help give a more accurate picture of the disease risk, particularly for those with borderline or slightly elevated lipid levels.

It has long been known that there is a subpopulation of people who even though they have normal or slightly elevated LDL cholesterol are at a high risk for heart attack, stroke etc. Elevated cholesterol definitely puts people at a higher risk for cardiovascular disease, but what about those with borderline or moderate elevations who develop heart and vascular disease?

Generally LDL cholesterol is not actually measured when standard blood lipid panels are done. It is calculated by a formula using measurements of total cholesterol, HDL cholesterol (the "good" cholesterol) and triglyceride. So the calculation just estimates how much cholesterol is in the LDL fraction.

Cholesterol is not free in the blood; it is contained in particles. The LDL particles in the blood are not all the same size or density. They have a size range, with the smallest being the most dense, and the biggest being the least dense. An analogy is comparing lead shot with a Styrofoam packing peanut. The lead shot is smaller but heavy; the Styrofoam is bigger and less dense.

The standard calculation of the amount of LDL cholesterol does not give an indication of the numbers of LDL particles. If there are lots of small dense particles, then the LDL cholesterol measurement might not be very high even though there are lots of particles.

The smallest densest particles are thought to be most atherogenic (most atherosclerosis causing) and most likely to cause cardiovascular disease, while the biggest and "fluffiest" are the least atherogenic.

So, considering lipid measurement. If there are lots of predominantly small dense particles in the blood, the calculated LDL cholesterol may not be really high since the small particles do not have very much cholesterol. However, the risk of cardiovascular disease may be significant, since there are actually lots of small dense LDL particles.

Since each LDL particle has one ApoB (apolipoprotein B100) on its surface, then the amount of ApoB can be used to estimate the number of LDL particles. So particularly if LDL cholesterol is borderline or slightly elevated then the amount of ApoB can give an estimate of the number of particles and from this the percentage of atherogenic small dense particles can be calculated.

The measurement of ApoB will therefore be particularly valuable for predicting which patients who though they do not have very high LDL cholesterol, are at risk of cardiovascular disease. These patients can then be given treatments to lower their cholesterol further, change the particles to larger less dense LDL particles, and can be routinely monitored for early detection of the development of heart and vascular diseases.

Judith Airey PhD. is a biomedical researcher with a range of interests including all things cardiovascular. She has several health-related websites including a blood pressure information site http://www.infobloodpressure.com/ and a blog http://www.lifeagingand.com/

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