But many doctors have despaired of finding an effective treatment in which, for people with raised but not sky-high cholesterol, the benefits outweigh the risks. The only effect of screening the group that doctors refer to as the 'worried well' may simply be to worry them sick.
Until recently, many assumed the answer was a change of diet. After all, in countries where they eat less animal fat, people have low cholesterol levels and a low incidence of heart disease. But a 1991 survey of 16 medical trials, published in the British Medical Journal, showed that only a dramatically different diet administered in a closed institution made an appreciable difference to individual cholesterol levels.
Drugs do an effective job, and prescriptions of them are increasing by 20 per cent every year. But here too the picture is clouded. The drug treatments seem to cause a small increase in deaths from other causes. A separate study, published in the British Medical Journal this summer, argues that only patients at very high risk of dying from coronary heart disease will benefit overall.
The question of when to use drugs causes heated arguments among doctors and patients' groups. They disagree, too, on the question of who should be screened. But it is hard to find anyone to defend roadside or do-it-yourself testing, other than those with a direct vested interest.
Hazel Connor may well owe her life to the test she took (prompted because her doctor noticed a characteristic thickening of her Achilles tendon). Even so, she is adamant that the test should only be done by the patient's own GP. In 1982 her cholesterol level was discovered to be 12.8 - more than double the level doctors think desirable. Further tests on family members revealed a shared genetic disorder - which explained a history of early death from so-called 'hardening of the arteries'.
Mrs Connor, aged 45, a receptionist from Bath, is chairman of the Family Heart Association - a self-help group for the one in 300 people whose livers overproduce cholesterol. Her work for the group takes her across the country. When, as often happens, she comes across high-street cholesterol testing, it does little for her blood pressure.
'I'd have those closed down right away. I don't like people being frightened. Yet they're queueing up. I've seen them doing a cholesterol level test with one hand and eating a sandwich with the other. It should be done through people's GPs.'
Testing could not be simpler. There are desk-top machines - priced upwards of pounds 400 - which rapidly analyse a blood sample taken from a thumb-prick. Models costing several thousand pounds can assess a patient's overall risk of heart disease when fed with extra data about age, weight, sex and lifestyle. However, unless these are carefully calibrated and operated by trained staff they can be inaccurate - surveys have shown levels of imprecision in GPs' surgeries as high as 7.5 per cent.
Last autumn, a statement from the British Heart Foundation attacked mobile screening units on the grounds that spurious results could give rise to unwarranted anxiety. But public demand for high-street testing is unabated. The Liverpool-based firm Health Beat has 20 mobile units on the road charging pounds 10 for a combined cholesterol and blood pressure test, using the relatively inexpensive 'Quickread' device.
Health Beat's director, Jim McGee, says: 'We cater for people who don't have time to visit their GP or who can't get a test from their GP. We provide a clean, accurate clinical test in under 10 minutes. If people are anxious, we spend up to 45 minutes reassuring them and putting the result in context.'
Now the high-street chemists have entered the cholesterol screening market. Boots now offers an American-made Home Cholesterol Test at pounds 7.99, which gives a result from a finger-prick of blood in under half an hour. The rationale is given in the accompanying leaflet. It says: 'Knowing your level may help you keep it under control.'
But will it? Kim Watson (not his real name) is a hard-working national newspaper cartoonist. Ten years ago he took a test at his GP's surgery as part of a routine check-up. His father survived a heart attack when in his mid-forties, but there was no family history of raised cholesterol. The result was 6.8 - well above the level of 5.2 considered desirable, but some way below the 7.8 figure at which drug therapy might be considered. With no other risk factors, this would be considered to put him at medium risk of heart disease.
Over the past 10 years Kim has become fluent in cholesterol-speak, ready and able to discuss the relative proportions of HDLs and triglicerides in his blood samples. He has cut down on meat and alcohol, is taking exercise and wondering about soluble fibre. He is entirely fit. His hospital consultant would like to see the level down to 6.4 - but in vain. 'The last test I had, it had gone up to 7.2. I'm a bit disappointed that it all doesn't make any difference.'
Dennis Dungworth, a Post Office vehicle mechanic aged 60, is also disappointed by the result of trying to change his diet. His cholesterol count was found to be 8.7, putting him, in theory, at high risk of heart disease when added to the fact that he is overweight. 'I do a heavy, physical job and I'm a knife-and-fork man. I do like a nice steak - but I've altered my diet as regards taking more fibre, having black coffee and lemon tea.' Yet the tests show no improvement, and he has failed to lose weight. Now his GP is considering drug therapy - a move Mr Dungworth would resist. 'My son's a chemist and one thing I know is that all drugs have side-effects.'
The difficulty for doctors is that although populations like Britain's, with high blood cholesterol, have high levels of heart disease, a cholesterol level is not in itself a good way to predict whether an individual will suffer from heart disease. There are other important risk factors, such as being overweight, smoking or a lack of exercise. Some argue that only patients with a combination of several factors should be given drugs - and that these might anyway get more benefit from tackling, say, smoking or a weight problem.
The catch is that when a patient who is at risk because of an unhealthy lifestyle discovers a raised cholesterol level, it is rarely sufficient to change a lifetime's habits. Health- conscious people may well also find they have raised cholesterol - but it is unlikely there are further lifestyle changes they can make.
Trevor Sheldon, a researcher at York University's Department of Health Economics, is worried that the net result will be that even more people go on drugs. The paper he jointly wrote for the British Medical Journal in May pointed out that current American guidelines would make a quarter of the middle-aged male population of the west of Scotland eligible for treatment. At this level, his paper suggests, more patients will die from the as yet incompletely understood effects of drug therapy than will be saved from death from heart disease.
Excess deaths among patients on cholesterol-lowering drugs have been attributed by some authors to heart disease and liver failure and also, mysteriously, to an increase in accidents and suicides - perhaps as a result of mood changes. Sheldon says: 'The newest class of drugs are the ones called the statins, and there's a really startling increase in the rate at which they're being prescribed. But they've only been evaluated in one large clinical trial, and this showed a large increase in deaths among those who'd been given the drugs over those who hadn't.
'Of course this effect only shows up when you study groups of people rather than individuals. Soon after the study was published I was contacted by someone whose mother had been put on one of these drugs, while showing no symptoms, and soon afterwards was admitted to hospital with heart disease. In that case you wonder whether it was due to her already having heart disease or due to taking the drugs. But the excess deaths do appear to be significant and do appear to be linked with the drugs - you don't find them with patients who have managed to get their cholesterol down through going on a very severe diet.'
Meanwhile, in better-off parts of Britain, there is no let-up in the stream of anxious patients arriving at GPs' surgeries clutching a screening result. In his practice in Highgate, north London, Dr Jonathan Riddell meets former clients of mobile monitoring units, as well as purchasers of home-testing kits.
At his local hospital the heart specialists are against testing healthy patients. 'But try explaining that to someone who's come in for the first time,' he says. There's enormous pressure to do a cholesterol test - and if you get a level of, say, six, what do you do about it? We now have a lot of people with slightly raised cholesterol who are very worried about it. It's nightmarish.'
Dr Peter Jackson of the Royal Hallamshire Hospital, Sheffield, worked on the study which undermined the idea that diet was generally effective in lowering cholesterol. He thinks the saga illustrates a basic lesson. 'The first rule in doing screening is that you must have a safe and effective treatment available. If you don't, why screen? The whole thing is a massive indictment of the medical profession.'-
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