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."
