According to conventional wisdom, preventive medical care — including regular exams and screening tests designed to catch a disease or a health problem before it has a chance to spread - reduces costs and prolongs lives. But the facts are much less clear. Study after study has shown that preventive medicine adds to overall health care costs.

The reason is fairly straightforward: Testing everyone costs a great deal of money, and the diseases being screened for are usually fairly rare. The savings generated by early detection of these few instances of disease are far outweighed by the costs of testing large numbers of people.

• The Office of Technology Assessment (OTA) studied the cost-effectiveness of adding coverage for several preventive measures to the federal Medicare insurance program for the elderly, and it found that none cut costs.

• A separate study by the OTA found that only three kinds of preventive care save money: prenatal care for poor women, tests in newborns for certain congenital disorders and most childhood immunizations.

A study by the Rand Corporation found that preventive care had little effect on the health status of individuals. Economist Louise B. Russell examined three popular screening tests — for cervical and prostate cancer and high blood cholesterol - and found serious drawbacks with each.

• Over a lifetime, a woman is more likely to have a false positive from a test for cervical cancer than she is to get cervical cancer.

• Reducing cholesterol can reduce the incidence of heart disease, but studies do not show that it prolongs life.

>The fact that preventive care is not always cost-effective does not mean it is wasteful. Diagnostic tests that show freedom from disease may relieve patients' anxiety and reassure them of good health. Thus, preventive care is like a consumer good that creates benefits in return for a cost. It is not like an investment good that promises a positive rate of economic return. Source: John Merline, "Is Preventive Medical Care Worth the Cost?" Consumers' Research, June 1995.