Friday, June 15, 2007

Health screening as dangerous quackery

In A Day at the Races, the Marx Brothers’ 1937 classic, a generously unholstered matron, played by Margaret Dumont, threatens to leave the Standish Sanatorium because it cannot find anything wrong with her. “I’m going to someone who understands me, I’m going to Dr Hackenbush! . . . Why, I didn’t know there was a thing the matter with me until I met him!” she says. Hackenbush, played by Groucho, takes her money and feeds her pills intended for horses.

Some doctors suspect that today’s craze for screening is not so very different. Feeling healthy? Come and have a CT scan and we’ll soon find you’re not. It’s hard to escape the relentless plugging of health scans from pop-up ads on the internet to women’s magazines and even Men’s Health. We haven’t gone as far as the US, where CT scans are advertised on gantries over freeways, but the message is the same: a day spent being screened could save your life.

Rejecting this seductive patter may seem contrary, even Luddite. But screening can be dangerous. Companies offering scans imply that being screened will detect hidden medical problems so early that they can be nipped in the bud. The process is compared to giving the car a service or an MOT. Anybody failing to listen is selling themselves and their loved ones short. The presumption is that by acting now we can buy our way out of future ill-health and that it’s worth spending a lot of money to do it. When an American physician asked a group of 55-year-olds if they regarded cancer screening as an obligation, most said they did. Asked to choose between a whole-body scan and $1,000 in cash, 73 per cent went for the scan.

Exact UK figures are scarce, partly because the scanning companies are relatively new. But Prescan, who opened in London just eight months ago, say they have carried out an average of 25 full body scans a week at an average cost of 1,200 pounds — a total of 960,000.

But screening has a downside. At worst, it may increase your risk of disease. Equally, it could set you off on a conveyer-belt of ever more intrusive and unpleasant tests that will leave you poorer but no healthier. This month, the Committee on the Medical Aspects of Radiation in the Environment will discuss a draft report on the radiation doses from unregulated screening. The Department of Health asked it to investigate after warnings from bodies including the British Medical Association that scans could do more harm than good.

CT scans represent only about 6 per cent of the X-rays done in Britain, but are responsible for 40 per cent of the radiation exposure. A typical dose from a CT scanner is around 10 millisieverts per scan, 500 times as much as in a typical chest X-ray. That may be a price worth paying if the scan is being used to monitor treatment of a serious disease, but to expose healthy people to such high doses is hard to justify. The estimate is that a dose this high increases the lifetime risk of cancer by about one in 2,000. Are the benefits of CT scanning of healthy people greater than this? The scanning clinics’ response is that in 2 to 3 per cent of those scanned, some life-threatening abnormality is found. Sometimes they can be treated successfully. For these individuals, the benefit certainly exceeds the risks.

But for the generality, we simply don’t know. For every dangerous aneurysm discovered and dealt with, there are a plethora of what radiologists call “incidentalomas” — odd abnormalities that probably don’t matter but often need further investigations to make sure. In one US study of 1,200 body scans, nearly a third of patients were advised to have further tests, most of them unnecessary because there wasn’t anything wrong.

CT scans produce amazingly detailed images, and no two individuals are identical. As one American radiologist put it: “With this level of information, I have yet to see a normal patient.” Scanning clinics, well aware of these criticisms, have focused on magnetic resonance imaging (MRI) rather than CT scans. Prescan, for example, based in London, says: “CT scans have a very high incidence of false positives. In other words, when the scan does find something (which can be as high as 90 per cent of the time) it has to be investigated with further costly and often invasive procedures. “The finding is usually a benign tumour, cyst or scar tissue but the person has incurred the cost and the discomfort of further tests — plus the stress of waiting for results.” Peter Mace, the assistant medical director of BUPA, said that the private health insurance company does not offer whole-body scanning using either CT or MRI because the benefits have not been clearly demonstrated and the radiation dose — in the case of CT — is significant. “What we do do are closely focused scans on the heart, looking for evidence of calcium,” he said.

The rationale for this is that as hardening of the arteries develops, the amount of calcium detectable by CT scanning rises, and there are studies that correlate calcium scores with the risk of heart attacks. The issue is whether knowing this calcium score adds to the predictive value of the other risk factors for heart disease, such as cholesterol levels, blood pressure and smoking status. Last year the American Heart Association concluded that it did, but only in people at medium risk. In those of low or high risk, it adds no extra predictive value. “I think that there is a reasonable amount of evidence, and it is growing, that coronary calcium is important,” Dr Mace says. “What we haven’t got is evidence that knowing the coronary calcium score will make people live longer. But inferentially, using common sense, I believe that is true.”

Most people tend to see screening as an entirely benign procedure. But it is not. Muir Gray, for many years programme director of the UK National Screening Committee, puts it strongly. “All screening progammes do harm,” he said. “Some do good as well, and some do more harm than good.” For NHS screening programmes, strict rules apply. The disease being screened for must have an early stage, for which an effective treatment exists. There must be an effective test, shown to work in properly conducted trials, that does not throw up too many false results, either positive or negative. And the benefits in lives saved must exceed the risks.

Even when these criteria are met it is hard to be sure that a screening programme is justified, as the arguments over the effectiveness of breast mammography make clear. The claim is that breast cancer screening saves 300 lives a year in Britain, but critics contest it. Their reasons include a dearth of convincing blind trials, and that scans may pick up early tumours that never develop, causing unnecessary treatment.

Cervical screening is less contentious, and the NHS is now slowly implementing a bowel cancer screening programme. There is good evidence that the use of ultrasound to screen for aortic aneurysms — swellings of the blood vessels in the abdomen that can burst without warning — would be costeffective.

Private screening clinics do not need to satisfy such demanding criteria. They rely on the worried well — or, as one wag put it, the worried wealthy — to pay large sums of money for tests that have not been shown to be cost-effective or really to save lives. There is anecdotal evidence of patients for whom such a test does pick up something that matters — an aneurysm or a tumour. If it can be treated successfully, that is a positive outcome. If not, it may mean that someone has longer to live in the knowledge of an incurable disease.

The medical literature is short of any convincing evidence that MRI scans, used on healthy people, save lives — one reason why BUPA does not offer them, Dr Mace says. But companies such as Prescan, Preventicum and ScanandScreen do. A whole-body MRI scan at Prescan costs 1,090 pounds, or 1,390 if you add a CT scan of the heart. Prescan failed to respond to my requests for evidence that such scans do more than lighten a patient’s wallet. What we do know is that such scans do typically pick up medically significant findings in 1 to 2 per cent of healthy people tested.

In a proportion of these positive findings, something can be done. For example, the discovery of an aneurysm in the brain might justify life-saving surgery to repair it. But even then the situation is more complicated than it seems, as a team from the University of Edinburgh makes clear in the latest issue of the Journal of Medical Screening. For healthy people with no family history, the lifetime risk of a bleed from an aneurysm in the brain is 0.6 per cent. But aneurysms are found in about 2 per cent of people scanned.

That means that for every three found, less than one would ever have been a problem. But once an aneurysm is found, treatment is likely. If 1,000 adults were screened, 20 of them would be found with an aneurysm, only six of which would ever have bled. If all of these 20 were treated surgically, two would be dead, disabled or brain-damaged by one year after the operation, and in eight cases out of the 20 the operation would have been only partly successful, leaving a risk of a future bleed.

That makes the discovery of an aneurysm a far less positive thing than the scanning companies pretend. It would, in fact, face the patient with an agonising choice and a fair chance of being killed or disabled to treat a condition that might never have caused him or her any harm.

The Edinburgh team, led by Dr Rustam Al-Shahi Salman, are in little doubt. The balance of risks and benefits mean that brain MRI scans “cannot be recommended outside the context of a research study”. They go on: “Undoubtedly, further research is needed to establish whether whole-body screening is effective, although it would require a very large randomised trial. “Regulatory bodies in the UK should follow the example of others such as Health Canada and the Royal Australian and New Zealand College of Radiologists by stating their view on whether whole-body screening is appropriate.” MRI scans do have appropriate uses in screening. They are, for example, better at detecting breast cancer in young women than conventional mammography, and the National Institute for Health and Clinical Excellence recommends their use in women between 20 and 49 known to be at high risk of the disease because they carry a predisposing gene.

At the very least, the companies that offer whole-body scans should make it clear that the procedure is unproven and that there is no robust evidence to show health benefits from undergoing it. “Why not treat a loved one or a valued employee to the ultimate spring gift?” asks Preventicum on its website. Frankly, it’s a gift I would have no hesitation in turning down. I’d just as soon have a horse pill.



Just some problems with the "Obesity" war:

1). It tries to impose behavior change on everybody -- when most of those targeted are not obese and hence have no reason to change their behaviour. It is a form of punishing the innocent and the guilty alike. (It is also typical of Leftist thinking: Scorning the individual and capable of dealing with large groups only).

2). The longevity research all leads to the conclusion that it is people of MIDDLING weight who live longest -- not slim people. So the "epidemic" of obesity is in fact largely an "epidemic" of living longer.

3). It is total calorie intake that makes you fat -- not where you get your calories. Policies that attack only the source of the calories (e.g. "junk food") without addressing total calorie intake are hence pissing into the wind. People involuntarily deprived of their preferred calorie intake from one source are highly likely to seek and find their calories elsewhere.

4). So-called junk food is perfectly nutritious. A big Mac meal comprises meat, bread, salad and potatoes -- which is a mainstream Western diet. If that is bad then we are all in big trouble.

5). Food warriors demonize salt and fat. But we need a daily salt intake to counter salt-loss through perspiration and the research shows that people on salt-restricted diets die SOONER. And Eskimos eat huge amounts of fat with no apparent ill-effects. And the average home-cooked roast dinner has LOTS of fat. Will we ban roast dinners?

6). The foods restricted are often no more calorific than those permitted -- such as milk and fruit-juice drinks.

7). Tendency to weight is mostly genetic and is therefore not readily susceptible to voluntary behaviour change.

8). And when are we going to ban cheese? Cheese is a concentrated calorie bomb and has lots of that wicked animal fat in it too. Wouldn't we all be better off without it? And what about butter and margarine? They are just about pure fat. Surely they should be treated as contraband in kids' lunchboxes! [/sarcasm].

Trans fats:

For one summary of the weak science behind the "trans-fat" hysteria, see here. Trans fats have only a temporary effect on blood chemistry and the evidence of lasting harm from them is dubious. By taking extreme groups in trans fats intake, some weak association with coronary heart disease has at times been shown in some sub-populations but extreme group studies are inherently at risk of confounding with other factors and are intrinsically of little interest to the average person.


1 comment:

Lynne Eldridge M.D. said...

Thank you for addressing total body CT scans as a screen for disease in healthy individuals. In the U.S. these seem to be available in every city even though they have not been shown to be beneficial in increasing life expectancy. Yet, as you state, they do have the ability to lower life expectancy due to radiation induced cancer. The FDA has adviced against this practice which remains widely available. To demonstrate the significance of the dose of radiation from one elective total body CT scan in the U.S., a typical scan here results in the absorption of 13 milliSieverts of radiation. This is the dose of radiation one would have received standing 2.4 km from the center of the Hiroshima atomic bomb blast!

Lynne Eldridge M.D.
Author, "Avoiding Cancer One Day At A Time"