PREVENTIVE MEDECINE: IMPORTANT QUESTIONS ASKED ABOUT SCREENING
Are screening procedures likely to pick up the diseases that really matter?
This is difficult to answer but an examination of the results of ten major industrial health examination programmes in the US found that less than half of the people who subsequently died from cancer had the condition diagnosed at a screening examination, and slightly fewer than two-thirds of those who died from heart disease were identified prior to developing symptoms of lethal heart disease. Even if we do agree that picking up some people who are at risk from such serious disorders, and treating them ahead of time is valuable, regular screening appears to be a rather insensitive tool for the early detection of serious diseases.
Will the treatment of a risk factor really have an impact on the development of the disease?
It is all very well knowing that someone has an increased likelihood of, say, having a heart attack or stroke if he or she has high blood pressure but prevention is more complicated. Reducing blood pressure brings a marked reduction in the risk of having a stroke but, it seems, a much smaller reduction in the risk of having a heart attack.
Will people act on the results of screening?
Results from screening procedures are of no value in themselves-they have to be acted upon by someone. Any smoker knows how difficult it is to stop and every fatty how difficult it is to slim.
The results of the many studies that have examined how reliably patients take medication are sobering. Studies in Canada, for example, have found that ‘ambulatory patients are unlikely to take more than 50 per cent of the prescribed medications they receive from clinicians and the amount of knowledge which a patient possesses about his or her illness has almost no relation to that patient’s degree of compliance with therapeutic instructions’. So if people won’t or don’t take their medication or the advice the doctor gives, why bother to tell them what’s wrong in the first place? A study of high-blood-pressure patients found that those who were told they had the condition, following screening, had more sickness absence from work than those who weren’t told.
Do screening programmes really alter the outcome of disease?
Interesting research has come from the Kaiser-Permanante Group in California who randomly divided several thousand patients into two groups. The first group was encouraged to have regular health screening whilst the other used the medical services as and when they needed them. After seven years of study the results showed no advantage to those who were screened regularly-or rather no advantage for women and only a small one for men. Only men aged between 45 and 54 when they entered the trial showed differences in illness and absenteeism from work.
Perhaps of most significance is that of the 400 deaths occurring in the control group (those not given regular screening) during the experimental period only 15 per cent were judged to have been ‘potentially postponable’ with the best possible application of preventive medical treatment!
Are we evaluating screening tests properly?
Every disease has a natural clinical course and to a great extent the success doctors have with treatment depends on where in this process they catch the disease. Early diagnosis through screening will always appear to improve survival because screening will tend to detect patients in whom the disease has a long hidden (pre-clinical) stage. As a result conditions picked up during screening can expect to have a better outcome even if the treatment they receive has no effect at all.
Could screening actually be harmful in any way?
In our understandable desire to detect everything as early as possible it is easy to forget that screening has a potential for harm too. First, it costs an enormous amount in terms of both money and other resources to screen thousands or even millions of people, and the ratio of positive discoveries to cost can be very low indeed. This is closely linked to the fact that in a free society we cannot force people to be screened for most things. So it is that in certain conditions (notably cervical cancer) the people who come forward to be screened are the least likely to be at risk, while those who stay at home would be the most cost-effective group to be screened. In a society with finite resources for medical care-which is now the case in almost every country-such a ‘waste’ of money and resources must be a serious cause for concern.
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