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Know Your ApoB Levels?

Study finds marker predicts heart trouble better than cholesterol levels

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HealthDay Reporter

MONDAY, Oct. 27, 2003 (HealthDayNews) -- A new phrase may soon be added to the vocabulary of heart-conscious Americans: apolipoprotein B.

Blood levels of apolipoprotein B (ApoB) can be a better indicator of heart disease risk than the currently standard marker, LDL cholesterol (the "bad" kind that clogs arteries), says a report in the Oct. 28 issue of Circulation.

That report describes the results of blood tests and other measures of heart risk among 1,522 people in the Insulin Resistance Atherosclerosis Study, which examines the link between abnormal blood sugar metabolism and the development of heart disease.

Researchers measured levels of both LDL cholesterol and ApoB, which is a sub-unit of the LDL molecule. They also measured several other known risk factors for heart disease -- obesity, the inflammation-related molecule called C-reactive protein, clot-inducing molecules and insulin levels.

"In each statistically comparison, the elevated ApoB group had higher associated risk than the elevated LDL cholesterol group," the researchers report.

That's because not all LDL cholesterol is created equal, says Dr. Allan D. Sniderman, a professor of medicine at McGill University in Canada and one of the authors of the Circulation report.

LDL comes in particles of different sizes, Sniderman explains. Larger particles are much less likely to form the plaques that narrow and then block arteries than small, dense particles, he says. High ApoB levels are associated with higher concentrations of those small, dangerous particles.

"People with diabetes and other groups at high risk of heart disease can have normal LDL cholesterol levels but an increased number of small LDL particles," Sniderman says. "If you look at their LDL cholesterol, things can look OK. But what this study shows is that there are other things to consider as well."

High ApoB readings indicate the body is not metabolizing fatty acids properly, he says, "and we think that abnormalities of fatty acid metabolism at the end of the day are responsible for heart disease."

The issue now is how to include ApoB testing as part of the assessment of heart disease risk, Sniderman says. "It is a challenge in the best sense of the word, as how we can bring the benefits of new knowledge to patients without making it seem that we are contradicting past knowledge."

Canadian risk assessment guidelines were changed recently to include a recommendation for ApoB testing, as well as LDL cholesterol tests. U.S. guidelines drawn up by the American Heart Association and the federal National Cholesterol Education Program do not recommend routine ApoB tests.

That may change, says Alice Lichtenstein, director of the cardiovascular nutrition laboratory at Tufts University and a spokeswoman for the American Heart Association, but any change will not come overnight.

"Normally, guidelines are not altered on the basis of one study," Lichtenstein says. "Given the totality of evidence, there is a lot we have to look at. At this point, the data are very compelling, but it would be difficult for a physician to justify measuring ApoB levels until the guidelines change."

When and if they do change, there will be no major upheaval in medical practice, Sniderman says. ApoB testing is easily done, and elevated ApoB levels can be treated effectively with the same statin drugs now widely used to lower blood cholesterol levels, he says.

More information

The importance of blood cholesterol is described by the American Heart Association, which also has a page on other risk factors.

SOURCES: Allan D. Sniderman, M.D., professor, medicine, McGill University, Montreal; Alice Lichtenstein, Sc.D., director, cardiovascular nutrition laboratory, Tufts University, Boston; Oct. 28, 2003, Circulation

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