Beneficial And Adverse Effects Of Screening

Who will gain and who will lose on participating in a screening programme? Since the evaluation of screening programmes is often complex, especially when screening for risk factors, no simple and clear-

cut answers can be given. In part, it will depend on the ability of the chosen screening test to correctly separate those that will become ill from those that will continue to be healthy. In part, it will depend on whether the instituted early treatment on those classified to be at high risk is effective or not. In other words, whether the early treatment really prevents or postpones the target disease of the screening programme.

As mentioned earlier, screening for early disease has some advantages compared to screening for a risk factor. In screening for disease, e.g. breast cancer in women, most of the true positives and perhaps some of the false negatives will develop symptomatic disease. This makes it possible, even though not easy, to evaluate on an individual level the gains and losses that are at stake.

In screening for a risk factor, as in screening for hypertension or obesity, most of those screened to be at high risk will not, during a foreseeable time period, develop the target disease of the screening programme whether myocardial infarction, stroke or type 2 diabetes. In such a situation our ability to predict the outcome on an individual level is very limited.

Those who benefit most from participating in a screening programme are individuals in whom the serious consequences of the target disease have been prevented or postponed by the early treatment. This is also the reason why we do the screening in the first place. What about those screened to be at high risk, where serious consequences of the target disease do not develop, even if followed for a very long time. Psychologically, they may be in a lose situation. They have been alerted of a serious risk, without having cause to be alarmed, and may react with anxiety and depression. How much unjustified anxiety and depression is evoked in individuals participating in different screening programmes? The question is impossible to answer in any precise manner and has not received much attention in the evaluation of screening programmes.

A study examining potential adverse psychological effects of screening for cardiovascular risk factors showed that a minority (about 20%) of those screened to be at high risk reacted with some degree of anxiety and confusion (7). Another study, also examining adverse psychological effects of screening, found a mild degree of worry in people labelled as having high cholesterol levels when compared to those labelled as normals. However, the level of anxiety did not influence mood, participation in social activities or life satisfaction. The conclusion was that the screening did not create any adverse psychosocial consequences (8). A similar result was found in a study of screening for hypertension. Individuals with mild to moderate hypertension were compared to individuals with normal blood pressure. Assessment for psychological effects was made repeatedly during a 12-month follow-up. A self-administered questionnaire comprising general health issues was used. A diagnostic psychiatric interview was conducted if the questionnaire indicated a high risk of developing psychiatric manifestations. In the study, no support was given for the belief that the screening programme evoked psychiatric symptoms among the participants. In fact, the reverse was suggested. Based on the interviews, individuals treated for hypertension showed less anxiety than individuals not in the treatment programme. There may, of course, be several explanations for this effect. Regularly attending a clinic could be one explanation. There could also be anxiolytic side effects in the antihypertensive medications that were used (9).

What about those found to be healthy in a screening programme? As stated above, our ability to predict the outcome for an individual is very limited. On that account, there is reason to assume that some individuals classified by the screening test as normal may in fact have an increased risk of becoming ill (false negatives). A harmful effect of screening may also arise in a situation where an individual on testing is found to be without risk factors. A negative screening test may be regarded by the individual as a proof of being healthy and living a healthy life. Ideas of not overdoing things starts to rankle. The next step in the chain might be a worsening in the lifestyle of that individual. This justification for an unhealthy behaviour has sometimes been called the 'certificate of health' effect and must be considered an adverse effect of the screening programme (7).

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