Do You Really Need More Lipoprotein Tests?

Your doctor has probably ordered the standard lipid profile, a blood test used to measure your total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides.

These results also allow an estimate of harmful low-density lipoprotein (LDL) cholesterol, which is known to promote the formation of atherosclerotic plaques.

In addition to the lipid profile, some doctors order one or more of the following tests. Are they really necessary?

Here are some of the ways you can learn more about your blood lipoproteins:

• Lipoprotein (a). A measurement of the amount of lipoprotein (a) in the blood is often worthwhile because high levels of lipoprotein (a) are a risk factor for coronary heart disease.
• Apoprotein B. This is the only protein component of LDL and a major constituent of very low density lipoprotein (VLDL). Measurements of apoprotein B can be valuable in people who have normal LDL cholesterol levels but whose LDL particles are very small and more likely to cause atherosclerosis.
• Direct LDL measurement. This can be useful when high levels of triglycerides make it impossible to use results of the standard lipid profile to estimate the LDL cholesterol level.

There is good evidence that some forms (fractions) of LDL are more likely to cause atherosclerosis, while some HDL forms offer greater protection against atherosclerosis than others. Two other tests simultaneously measure a range of lipoproteins:

• NMR LipoProfile®. This test uses nuclear magnetic resonance techniques to measure intermediate-density lipoprotein (IDL), five subfractions of VLDL, three subfractions of LDL, and five subfractions of HDL. ("Subfraction" refers to LDL or HDL particles of a specific size and density.) This profile is the more useful and widely used of these two tests because it provides the quantity of each lipoprotein subfraction, whereas the VAP test (below) only gives the relative amounts of each subfraction.
• VAP (Vertical Auto Profile). In this test, ultracentrifugation techniques quantify total cholesterol, triglycerides, and HDL cholesterol, just like a lipid profile. This test also measures lipoprotein (a), LDL cholesterol and VLDL cholesterol, and provides an indirect measurement of the relative amounts of IDL, two HDL subfractions, and several subfractions of VLDL.

These tests can be useful in choosing the best treatment for a minority of patients with abnormal lipid levels. But many doctors order one of these two tests routinely on all of their patients. I don't believe either test is necessary for most people and certainly discourage their use as a routine screening procedure.