Blood pressure and cholesterol levels are not the most accurate way of assessing the risk of heart attack and stroke, doctors believe.
Instead, measuring calcium build-up in the arteries gives a better indicator of the likelihood of heart problems, they say.
In comparison, the traditional ways of assessing who should be prescribed preventative drugs such as statins are inaccurate.
It means that tens of thousands of patients at low risk of a heart attack or stroke could be taking the drugs needlessly.
People with little or no calcium deposits in the arteries detected on CT scans are unlikely to suffer a heart attack or stroke, a study found. But doctors may have prescribed them statins based on other factors. The study suggests up to a third of patients were taking them unnecessarily.
Scans found that their coronary artery calcium (CAC) score – a formula based on the level of calcium deposits, age and gender – was actually low and they only needed advice on lifestyle.
The US research also revealed that one in six people believed to be at low risk had high scores, meaning they could benefit from taking drugs.
Calcium build-up in the arteries marks the calcification of plaque, which results in hardening that can lead to heart attacks.
The latest study, published in the European Heart journal, adds to mounting evidence about the value of calcium scans in predicting heart attack risk. The technology is little used in the NHS, where there is limited availability of expensive scans, but widely used in private clinics. Instead patients mostly have their risk calculated on family history, medical factors such as cholesterol and blood pressure levels, and lifestyle habits.
Study leader Dr Michael Silverman, a cardiology fellow at Brigham and Women’s Hospital in Boston, in the US, said calcium testing is superior in predicting heart attacks and deaths.
He added: ‘We showed that by using only the traditional risk factors, we miss a significant percentage of individuals at high risk. We may also be over-treating a large number of people who can safely avoid lifelong treatment.’
Calcium screening uses a CT scan to directly measure deposits in heart arteries, which are early signs of ‘furring up’ of the arteries.
This is converted into a score ranging from zero for no deposits into the hundreds. The higher the score, the greater the chances of an event such as heart attack or stroke in the next seven years.
Drug treatment usually starts at a score of 50-100, while bigger scores might lead to further tests of heart and artery function.
The study used data from almost 7,000 participants in the Multi-Ethnic Study of Atherosclerosis (MESA), who were given risk scores according to the traditional medical factors.
They were also given a coronary calcium scan and a CAC score.
The MESA participants did not have evidence of heart disease when they joined the study between 2000 and 2002. They were followed for around seven years for coronary heart disease events, such as heart attacks.
Roger Blumenthal, professor of medicine and director of the Johns Hopkins Ciccarone Center, and co-author of the study, said ‘We found that 15 per cent of people believed to be at very low risk actually had high coronary artery calcium scores above 100 and were at relatively high risk of a cardiac event over the next seven years.
‘On the other hand, 35 per cent of study participants thought to be at very high risk and needing aggressive therapy with aspirin and statin medication actually had no coronary artery calcium and an extremely low event rate of the next seven years.’
Dr Khurram Nasir, the study’s senior author, said: ‘Our study shows that coronary artery calcium testing holds promise as a frontline assessment for people before they develop heart disease symptoms.’
London cardiologist Dr Duncan Dymond said: ‘Calcium screening is widely used in private medicine but hardly at all in the NHS, which doesn’t have the resources to give people an individual and much more accurate assessment of their risk.’
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