Screening Does Not Save Lives Except in Very Few Exceptions

Screening for deadly illnesses does not necessarily save lives despite assumptions otherwise, according to a study published in the International Journal of Epidemiology.

The authors examined the results of screening for 19 diseases to determine whether or not screening actually helped to prevent death. Patients were asymptomatic when tested. They found that, screening decreases mortality in only a few circumstances.

“Screening for diseases that can lead to death typically does not prolong life substantially,” John Ioannidis, MD, DSc, the C.F. Rehnborg Professor in Disease Prevention at Stanford and senior author of the study, said in a statement. “A few screening tests may avert some deaths caused by the disease being screened, but even then it is difficult to document an improvement in overall survival.”

When choosing diseases to study, the researchers focused on cancer and heart and vascular diseases, as well as type 2 diabetes mellitus and chronic obstructive pulmonary disease, because mortality is a common outcome for these diseases. Diseases/disorders they did not include fell into the following clinical categories: infectious diseases; mental health conditions and substance abuse; metabolic, nutritional and endocrine disorders (except type 2 diabetes); musculoskeletal disorders; injury and violence; vision and hearing disorders; obstetric and gynaecological conditions; and miscellaneous (except chronic obstructive pulmonary diseases).

The only tests that reduced the number of deaths caused by the diseases studied were ultrasound for abdominal aortic aneurysm in men, mammography for breast cancer, and fecal occult blood test and flexible sigmoidoscopy for colorectal cancer.

The authors conjecture that the tests that failed to reduce mortality may not be able to detect the early stages of a disease accurately enough. Another factor may be the availability of life-saving treatments.

However, even if screening does not save lives, it might ward off other ill effects of disease, according to Dr Ioannidis.

“Screening may still be highly effective (and thus justifiable) for a variety of other clinical outcomes, besides mortality,” the authors concluded in their paper. "However, our overview suggests that expectations of major benefits in mortality from screening need to be cautiously tempered.”