LONDON (AP) - A new blood test may allow more accurate predictions of a person's risk of a fatal heart attack, scientists say.

A study published this week in The Lancet medical journal suggested the test, which measures levels of the protein part of cholesterol, may be a better predictor of heart trouble than traditional cholesterol tests and may one day lead to more tailored treatments.

High cholesterol is considered one of the strongest risk factors for developing coronary artery disease and dying from a heart attack, but some people develop heart trouble despite apparently normal levels of HDL and LDL cholesterol.

Experts say the new test, which involves measuring levels of cholesterol components called apolipoproteins, will fine-tune traditional cholesterol testing.

Apolipoprotein A-1, or apoA-1, is the protein part of HDL, the good cholesterol, while apolipoprotein B, or apoB is the protein in LDL, the bad cholesterol.

In the study, led by Dr. Goran Walldius of the drug company Astra Zeneca, researchers measured the blood concentration of the apolipoproteins as well as the traditional triglycerides, total cholesterol and LDL cholesterol in 175,553 Swedish people and followed them for five and a half years, on average.

By the end of the study, 864 men and 359 women had died of a heart attack.

The steepest increase in risk of heart attack related to cholesterol protein levels was seen when comparing those with the worst profiles with those with the best.

Men who had the highest levels of apoB, the bad protein, combined with the lowest levels of apoA-1, the good protein, were nearly four times more likely to suffer a fatal heart attack than those who had the lowest concentrations of the bad protein and the highest of the good protein. A similar pattern was seen for women, the study found.

The researchers found that measuring levels of apoB, attached to the bad LDL cholesterol, predicted fatal heart attacks more accurately than simply measuring LDL.

ApoA-1, the good cholesterol protein, seemed to protect against heart attacks.

Also, the higher the ratio of bad protein to good protein, the more likely someone was to later die of a heart attack.

"This is perhaps the largest study to date demonstrating that the ratio of apoB to apoA-1 may offer better predictive value for the development of coronary disease than most other data we commonly track," said Dr. David A. Meyerson, a Johns Hopkins University cardiologist and American Heart Association expert who was not connected with the study.

"We may now be at the threshold where this should be a routine measurement," he said.

The researchers noted a few apparent advantages of the new test. It was good at predicting later fatal heart attacks in people whose cholesterol tests were normal. Also, it worked just as well in young as old people. Traditional cholesterol tests are not found to be useful for people over 70.

The apolipoproteins could also eventually become the target of new drugs, experts say.

Scientists do not yet know what level of apolipoproteins should be considered normal or at what point patients should be given drugs to improve their profiles.

"Studies need to be done on whether treatments aimed at changing the apolipoprotein levels will work better at preventing the progression of heart disease than our current drugs," Meyerson said.

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