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Blood tests no better at predicting heart attacks

/ Source: The Associated Press

New blood tests that doctors hoped would more accurately predict which patients are headed for a heart attack or stroke are no better than cholesterol levels, blood pressure and other conventional measurements, a study found.

Doctors in recent years had become excited over substances in the blood that appeared to be powerful new predictors of a heart attack. These substances included C-reactive protein, or CRP; homocysteine; and BNP, or B-type natriuretic peptide.

An increasing number of family doctors have been ordering expensive tests for these substances, and some patients have started requesting them, in hopes of identifying people who do not have the standard risk factors but are still likely to suffer a heart attack or stroke.

But the new research, by scientists at the highly regarded Framingham Heart Study, found that tests of CRP, BNP, homocysteine and seven other substances are only a couple of percentage points better at predicting outcomes than the standard, commonsense risk factors that doctors have known for decades.

The difference in accuracy was considered so small as to be negligible.

“It’s a little bit disappointing,” said lead author Dr. Thomas J. Wang, a Harvard Medical School assistant professor. “I think our study and some other recent studies have begun to dampen that enthusiasm.”

No 'magic blood test'

The study was published in Thursday’s New England Journal of Medicine.

The Framingham researchers, who have been testing residents of the Boston suburb for several decades, used frozen blood samples taken from 3,209 healthy Framingham participants in the mid-1990s, then checked to see who had major heart complications or died over the following decade.

The best predictors were tests for BNP, CRP, homocysteine and renin in the blood and albumin in the urine. Patients with the highest levels of BNP and albumin were nearly twice as likely as those with lowest levels to suffer a heart attack, stroke or heart failure; those with the highest levels of CRP, BNP and the three other substances were four times as likely to die during the decade.

However, the standard risk factors — high blood pressure, high cholesterol, family history, advanced age, smoking, obesity, lack of exercise and diabetes — were just as accurate as predictors.

“This really supports the value of focusing on risk-factor reduction, not looking for a magic blood test,” said Dr. Richard Stein, director of preventive cardiology at Beth Israel Medical Center in New York. He predicted some insurance companies will soon start telling doctors to limit such tests, which are not covered by some insurers.

“At present, I don’t think we should be measuring these in routine clinical practice,” said Dr. Daniel Levy, director of the Framingham study, which is funded by the National Heart, Lung, and Blood Institute.

Risk factors really matter

Levy and Wang said the 10 “biomarkers” tested in the study may still be useful for the many patients at intermediate risk of heart problems — those determined by the conventional risk factors to have a 10 percent to 20 percent chance of suffering a heart attack or stroke over the next decade.

Dr. Sidney Smith, former president of the American Heart Association and director of the Center for Cardiovascular Science and Medicine at University of North Carolina, noted the findings may not apply to minorities. The Framingham residents are almost all whites of European extraction.

He said the findings also show that doctors and patients should work harder to get known risk factors such as obesity and diabetes under control to prevent serious heart problems.

Some doctors said they expect better blood tests to be discovered eventually.

“The question is, ‘Where’s the next frontier?”’ Levy said.

He said the answer could come from two huge federal studies. One, with results expected next year, is examining about 500,000 genetic variations in 10,000 people to spot differences linked to heart disease; the other, still being planned, will examine about 150 biomarkers to see which ones best predict future heart problems.