High blood pressure can be a sign of problems

University of Bristol researchers examined the accuracy of the Framingham risk equation in 6,643 healthy men.

The equation predicted 4.1% would die from heart disease within ten years, but in reality just 2.8% actually did - an over-estimation of 47%.

The research is published in the British Medical Journal.

It is important that people are not prescribed medications unnecessarily and that others who have been previously overlooked are now correctly identified. Dr Charmaine Griffiths

The formula was even less accurate when applied to the risk of having any type of heart attack.

It predicted 16% of men would have a heart attack within 10 years - a 57% over-estimation of the true figure of 10.2%.

The researchers say the main problem is that the test is based on figures that are out of date, as rates of coronary heart disease are falling.

The statistics used in the equation are taken from a major investigation into the levels of heart disease conducted between 1968-1975.

Different risk levels

However, the formula also fails to take full account of the fact that risk varies between different regions, ethnic groups and socio-economic classes.

They say a simple adjustment to the equation would make it much more accurate.

But they warn that in its current form, use of the formula may undermine a patient's ability to make an informed choice about starting preventative treatment, and may cause unnecessary anxiety.

They also warn it may affect life insurance premiums, and lead to unnecessary spending by the NHS on drugs that are not needed.

In a BMJ editorial, Professor Hans-Werner Hense, from the University of Munster, Germany, said the ability to assess risk was a potentially very useful aid for doctors.

But he said: "What it takes to foster confidence in its application, however, is up to date epidemiological data - collected in surveys, registers, and when possible, cohorts from populations with varying risk levels - that can be used regularly to adapt predictions."

Dr Charmaine Griffiths, of the British Heart Foundation, told BBC News Online: "The results of this study highlight the need for an accurate, standardised screening process or risk assessment to ensure that those at risk of coronary heart disease are accurately identified.

"It is important that people are not prescribed medications unnecessarily and that others who have been previously overlooked are now correctly identified."

Someone suffers a heart attack every two minutes in the UK.

The national service framework for coronary heart disease in England and Wales states that people whose estimated risk is at least 30% over 10 years should be offered treatment.