Cholesterol screening is a regular part of lifestyle and well-person
assessments in the workplace. But although it is recognised that raised
cholesterol levels lead to coronary heart disease, the benefits of random
screening are still being questioned.Â
By Vicki Madden
The advantages of lowering cholesterol have already been demonstrated in two
landmark studies. The large scale secondary prevention clinical trial, the
Scandinavian Simvastatin Survival Study(4S)1, showed that patients with proven heart
disease and a raised total serum cholesterol in the range 5.5 to 8 mmols/litre
benefited from treatment with the lipid lowering drug, simvastatin.
Compared with placebo, those in the treatment group had a 30 per cent
reduction in all cause mortality, and a 40 per cent reduction in CHD mortality.
These survival benefits were also seen in men over 60 years of age and in
women.
The other large landmark study, the West of Scotland Coronary Prevention
Study (WOSCOPS) found that patients with raised cholesterol but no previous
history of CHD also benefited from cholesterol lowering treatment.
Results of the five-year study showed that those offered lipid lowering
therapy had a 31 per cent reduction in non-fatal heart attacks, compared with
those in the placebo group2.
National diet
Coronary heart disease rates in different countries reflect the serum
cholesterol levels of their populations and these, in turn, are linked to
national diet.
Countries where most energy is derived from carbohydrate have the lowest
cholesterol levels and those, such as Britain, with the highest cholesterol
levels consume a diet rich in fat.
In Britain, the median cholesterol level from middle age onwards is 6 to 6.5
mmols/litre, and while the levels are dropping among the young and more
affluent, Britain still has one of the highest CHD rates in the world.
Although different groups of cardiologists recommend slightly different
cholesterol levels at which diet and/or treatment should be initiated, all tend
to be much lower than a few years ago.
The most recent Joint British Recommendations on the Prevention of CHD in
Clinical Practice (1998) propose that for patients with established heart
disease, total cholesterol should be maintained at below 5.0 mmols/litre and
the "bad" low density lipoprotein (LDL) cholesterol should be
maintained at below 3.0 mmols/litre3.
In practice, as so many people are above these levels, screening programmes
are not recommended for everyone.
Marilyn McDougall, health promotion nursing adviser at Glaxo Wellcome,
screens patients who opt for a lifestyle assessment. "As part of the
assessment we do a finger prick analysis for total serum cholesterol," she
said. "If anyone has a level over 6.5 mmols/l we recall them for a fasting
cholesterol level and then send off their blood to the hospital for further
analysis. We also refer them to their GPs."
She adds, "Those with levels between 5.5 to 6.5 mmols/l are given
leaflets on cholesterol and advice on diet and exercise. In six years we have
had nine men and four women with levels over 6.5 mmols/l. When they were
recalled for their second assessment, we found all the men had cholesterol
levels over 6.5 mmols/l, but only two women. Of the two women whose cholesterol
levels had fallen, one had been put on hormone replacement therapy and the
other had been put on lipid lowering therapy."
False negatives
Although screening such as this is common in occupational health departments
around the country, epidemiologists such as Professor Nick Wald and Dr Malcolm
Law, from the Department of Epidemiology, St Bartholomew’s Hospital, London,
still question the benefits. "Random testing like this will only pick up
around 11 per cent of those with raised cholesterol, and of these as many as 5
per cent may be false negatives," says Dr Law.
"Unlike breast cancer screening, cholesterol screening is not a
sufficiently discriminating test. The difference between those at high risk and
those at low risk of developing CHD is small.
"You cannot assume that people with cholesterol levels of 5.2mmols/l
have no risk of developing CHD. It’s like telling someone who smokes 30
cigarettes a day that he has a higher risk of developing cancer than someone
who smokes 20 a day. The difference in their risk is, in fact,
negligible."
However, Dr Law concedes that the mere fact of screening someone may
motivate them to change their way of life. "If they have a cholesterol
test they may then follow the health advice that will accompany the screening
test.
Graham Johnson, occupational health manager at MTL Medical Services, is also
sceptical about random cholesterol testing. He says it has just completed a
major contract with 750 personnel from Mersey Police.
"The computer-aided lifestyle package that we used included a random
cholesterol test. During the course of the tests, this threw up a number of
individuals with raised total serum cholesterol. As this gave no indication of
their LDL/HDL ratio we had to refer them to their GP for further fasting
cholesterol testing. "Inevitably, some individuals with raised total
cholesterol became unduly anxious."
Johnson recommends all those with high total serum cholesterol are also
given a fasting cholesterol check. Cholesterol should not be considered in
isolation, he adds, and other CHD risk factors such as smoking, blood pressure,
and the amount of exercise an individual does must be taken into account.
"Whatever else it does, the cholesterol test can make individuals
reflect on their lifestyles. It can only be to the good if that means that they
take more exercise and change their diet."
Vicki Madden is a freelance medical writer
References
1 Randomised trial of cholesterol lowering in 4,444 patients with CHD: the
Scandinavian Simvastatin Survival Study(4S). Scandinavian Simvastatin Survival
group. Lancet 1994;344:1383-9.
2 Prevention of CHD with pravastatin in men with hypercholesterolaemia.
Shepherd J, Cobbe SM, Ford I, et al for The West of Scotland Coronary
Prevention Study Group. New Engl J Med 1995;333: 1301-7
3 Prevention of CHD in clinical practice: recommendations of the joint
second task force of the European and other societies on coronary prevention,
Eur Heart J 1998;19: 1434-1503.
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Links
British Heart Foundation: www.bhf.org.uk
British Heart Foundation Health Promotion Research: www.dphpc.ox.ac.uk
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