Screening people for diseases doesn't necessarily save lives, study shows

It seems like it should work: If everyone were tested for every disease, lives would be saved, right? These conditions would be spotted quickly, treated, and voilà: The deadly illness would be vanquished.

As it turns out, this isn’t necessarily the case, according to a new study by researchers at the School of Medicine. 

“Screening for diseases that can lead to death typically does not prolong life substantially,” said John Ioannidis, MD, DSc, the C.F. Rehnborg Professor in Disease Prevention at Stanford and senior author of the study. “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.”

The lead author of the study, published online Jan. 15 in the International Journal of Epidemiology, is Nazmus Saquib, PhD, a former postdoctoral scholar at Stanford.

Ioannidis and his team examined the results of screening for 19 diseases to determine whether screening helped prevent death. The researchers looked at evidence from randomized, controlled trials and from meta-analyses combining the results of the trials. Patients were asymptomatic when tested.

The researchers found that screening decreased mortality in a few circumstances: ultrasound for abdominal aortic aneurysm in men, mammography for breast cancer, and fecal occult blood test and flexible sigmoidoscopy for colorectal cancer. But no other tests reduced the number of deaths caused by the 19 diseases.

Why?

The test might not be able to detect accurately enough the early stages of a disease, or there might not be lifesaving treatments available, the study said.

Ioannidis acknowledged that screening might ward off other ill effects of disease, aside from death. But in general, few screening tests among the many new ones being proposed are subjected to a randomized, controlled trial before they are introduced, he said.

“This is unfortunate,” said Ioannidis, who is also director of the Stanford Prevention Research Center. “All screening tests should be evaluated with rigorous, randomized, controlled trials. I see no alternative to prove that they are worth being adopted in large populations.”

This study followed another recently published paper in which Ioannidis and colleagues argue that screening all baby boomers for hepatitis C isn’t necessarily beneficial.

The study’s other co-author is Juliann Saquib, PhD, a former postdoctoral scholar at Stanford. 

The study was supported in part by a grant from the National Heart, Lung and Blood Institute.