TORONTO - Measuring the ratio of two forms of proteins in the blood is superior to cholesterol testing as a means of predicting heart attack risk and should become part of standard practice by doctors, researchers say.
In a study published in this week's edition of The Lancet, a Canadian-led international research team found that the ratio of fat-binding proteins - known as ApoB and ApoA1 - account for a significantly higher proportion of heart attack risk than do elevated cholesterol levels.
The research, which grew out of the groundbreaking 2004 INTERHEART study to determine heart attack risk factors, involved analysis of blood samples from almost 22,000 participants in 52 countries.
Its main finding: the ApoB-ApoA1 ratio accounted for 54 per cent of the risk of heart attack, whereas the ratio of total cholesterol to good cholesterol (HDL) accounted for 32 per cent of that risk.
"The ApoB-ApoA1 ratio was superior to any of the cholesterol ratios for estimation of the risk of acute heart attack in all ethnic groups, in both sexes and at all ages," principal investigator Dr. Matthew McQueen, a professor of pathology and molecular medicine at McMaster University, said Thursday from Hamilton.
"And it should be introduced into worldwide clinical practice."
ApoB and ApoA1 are two types of apolipoproteins. They form part of spherical particles that transport dietary fats, such as the so-called bad cholesterol LDL, through the bloodstream. A high ratio of LDL to HDL can cause plaque to form inside the blood vessels, leading to cardiovascular disease and boosting the risk of heart attack and stroke.
ApoB is the main structural protein in these particles that allows LDL molecules to circulate in the bloodstream.
McQueen said that measuring cholesterol ratios doesn't reveal how many of these particles are delivering fat molecules within the blood - but testing for ApoB does.
"If we see somebody who has got the LDL cholesterol at apparently reasonable levels, but the ApoB is still elevated, we should continue to push with the treatment to get lower levels still, so we reduce the number of bad molecules," he explained.
Many patients must take cholesterol-lowering drugs for life and need to have their blood-fat levels tested regularly.
McQueen said ApoB-ApoA1 ratio testing would not only be more effective, but it also would be easier for patients because, unlike cholesterol testing, no 12-hour fast is required beforehand.
"We actually believe that this ratio should replace the total cholesterol to HDL cholesterol ratio because it is giving us everything that that ratio gives, but more."
In a commentary accompanying The Lancet study, Dr. Lars Lind of University Hospital in Uppsala, Sweden, says apolipoproteins can be measured in a standardized and automatic manner at a similar cost to conventional cholesterol analysis.
He writes that substituting cholesterol tests with those analyzing apolipoprotein ratios would "be a demanding but not impossible task."
