SUMMARY

Mass screening of healthy populations is a type of early detection of diseases and risk factors applied in secondary and primary prevention, respectively. Of course, the goals of prevention are beneficial but we should not forget the potential adverse effects on the health of the scrutinized populations.

First, the preventive activities within the context of the health system are considered. Their main functions are promotion, protection and caring for people’s health. These goals are not exclusively achieved by the health care system but also by society as a whole, particularly health promotion. Because health determinants are basically found in the community, direct health care system interventions have access to them very seldom. Health protection is also a goal for many other social sectors, as well as the health sector. Thus, sanitation and environmental safety, as well as the control of traffic, occupational, home, and food safety and so on, require the implication of non-health system agents. Other social sectors must contribute to health care activities as well as the health sector. In this context, prevention can be improved from a comprehensive and integrated perspective in which health activities should be complementary to community activities.

Then, we analyze the logic of early detection, which is based on the natural history of disease. This simplified scheme of the disease process in individuals makes it is easy to apply one of the prevention modalities, primary, secondary and tertiary, depending on the appropriate moment of its natural history to apply it. The idea of early detection has been a change of the traditional medical perspective, whose first historical justification was to aid sick people. Thus, early diagnosis is the means to discover and select those people that can take full advantage from the early treatment of disease, which is, properly, the preventive intervention. However, screening is increasingly used to discover the exposure to risk factors such as hypertension, hypercholesterolemia or osteoporosis, which are not diseases, strictly speaking. This extension of early detection is another change in the clinical perspective, and therefore, requires other rules than those applied by medicine when the assisted people are actually affected by disease, limitations and suffering. It is very important to include safety aspects among these new rules not only because these interventions are addressed to people who do not know they have a particular illness but because they actually do not have any disease. In many aspects, the recommendations made by Wilson and Junger in 1968 are current ones.

Procedures of early detection or diagnosis can be applied in many ways, as selective or opportunistic ones, case findings, or as a part of a formal program addressed to the general population or specific groups of this population whether they are or are not users of health services. These procedures are based on tests administered to classify people in two categories: affected, or at least suspected of being affected, and not affected. They can be applied alone or together with other tests when the purposes are to detect more than one characteristic and it is possible to implement them in different situations.

There are multiple limitations. Some of them are related with pertinence, because their use is not always justified in all of the situations when it is physically possible to carry them out. Some others depend on the degree of efficacy they can achieve and finally yet importantly, their applicability must be warranted in the real world. In any case, preventive interventions can provoke adverse effects and a systematic evaluation should be made.

To conclude, it is very convenient to specify, from the health system and from society, the pros and cons of this kind of activities, until a new social contract between society and the health system can be established to define the responsibilities and commitments of both.