It seems like it should work: If everyone was tested for every disease, lives would be saved, right? These conditions would be spotted quickly, treated and voilà - the deadly disorder would go away.
Not necessarily, according to a new study from a team led by Stanford epidemiologist John Ioannidis, MD, DSc, published this week in the International Journal of Epidemiology. Here's Ioannidis:
Screening for diseases that can lead to death typically does not prolong life substantially; 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.
Ioannidis and his team examined whether screening prevents death in 19 diseases with 39 screening tests, looking at evidence from randomized controlled trials and from meta-analyses combining the results of the trials. Patients were asymptomatic when tested.
In their meta-analysis, the researchers found that mortality from the disease dropped in these cases: ultrasound for abdominal aortic aneurysm in men, mammographyfor 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 disease in meta-analyses.
What gives?
The test might not be able to detect accurately enough early stages of the disease, or there might not be life-saving treatments available, Ioannidis and colleagues write.
Ioannidis acknowledges 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, Ioannidis said.
"This is unfortunate. 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," he told me.
This work follows another recently published paper, in which Ioannidis and colleagues argue that screening all baby boomers for hepatitis C isn't necessarily beneficial.
Previously: To screen or not to screen for hepatitis C, Bad news for pill poppers? Little clear evidence for Vitamin D efficiency, says Stanford's John Ioannidis, John Ioannidis, MD: Research's researcher and Screening could slash number of breast cancer cases
Photo by david_jones
