At a time when prevention is being hailed as a key to health reform, indeed required as an essential health benefit, new evidence is questioning assumptions about the benefits and costs.
Does screening for disease in asymptomatic adults save lives? That's the question Stanford epidemiologist John Ioannidis, MD, and colleagues asked as they reviewed 48 randomized control trials and 9 meta-analyses on 39 screening tests for 19 diseases, including cardiovascular disease, Type 2 diabetes, abdominal aortic aneurysm and cancers of the breast, cervix, colon, lung, ovarian and prostate.
Their answer is that screening people who are not symptomatic generally does not save lives, with a few exceptions. They found evidence of a reduction in mortality in 30 percent of the disease-specific areas, and only 11 percent of the all-cause mortality estimates in randomized trials.
"Screening for diseases that can lead to death typically does not prolong life substantially," Ioannidis said in a Stanford media release. "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."
Prevention through lifestyle changes may prove valuable for the health of the American population, such as the federal government's Million Hearts campaign to promote healthy eating and exercise, and the Tips From Former Smokers advertising series.
But many preventive disease screenings may be of limited value on an individual and collective basis, and even may be harmful -- exposing patients to false positives, biopsy complications and unnecessary treatment and contributing to excessive national healthcare spending.
Across the data on preventive screenings, Ioannidis and his colleagues found little evidence of lives being saved.
"Documented reductions in disease-specific mortality in randomized trials of screening are uncommon," they wrote in the International Journal of Epidemiology.
"Reduction in all-cause mortality is even more uncommon in single trials and has not been documented in the latest available meta-analysis of multiple trials for any of the examined topics," they concluded. (At right, an ad by Ingalls Health System in suburban Chicago.)
Among the screenings they studied, four do show evidence of benefit in terms of reducing mortality and adding years to an individuals life -- ultrasound screenings for abdominal aortic aneurysms in men, mammograms for breast cancer in women, and fecal occult blood tests and flexible sigmoidoscopies for colorectal cancer. (There have been no randomized controlled trials measuring the effectiveness of colonoscopies, considered gold standard in colon cancer.)
Ioannidis and colleagues found that those tests were associated with reductions in disease-specific mortality ranging from 16 percent to 45 percent.
Marketing a test with risks
Screening for disease is a complicated issue and also one that can tap into natural human concerns for their own longevity -- something hospitals are using as they market lung cancer screenings for 30-year smokers, who under a recent U.S. Preventive Services Task Force decision are eligible for no- or low-cost CT scans.
But they are also complicated in that they can lead to patient harm and overuse. The U.S. PSTF's B rating for CT scans in certain at-risk populations could lead to Medicare alone spending more than $9 billion over five years, according to a study a in the Journal of Clinical Oncology.
And at least a portion of that will be spent on former-smokers who without screening might end up living years before dying of other causes, according to researchers who reviewed data from the National Lung Screening Trial, the study that guided the U.S. PSF's decision.
More than 18 percent of all the lung cancers detected by low dose CT scans in the trial "seem to be indolent" and "clinically insignificant," wrote Duke University Medical Center radiologist Edward Patz Jr, MD, and colleagues, in JAMA Internal Medicine.
"Screening for lung cancer has the potential to reduce mortality, but in addition to detecting aggressive tumors, screening will also detect indolent tumors that otherwise may not cause clinical symptoms," they wrote. "These overdiagnosis cases represent an important potential harm of screening because they incur additional cost, anxiety, and morbidity associated with cancer treatment."
William Tierney, MD, the CEO of the Regenstrief Institute and medical professor at Indiana University, makes a more blunt argument: "Paying for widespread CT screening to detect lung cancer among smokers is not smart."
Beyond lung cancer screening, Stanford's Ioannidis and colleagues argue that there is more uncertainty than reliable knowledge.
A combination of factors probably contribute to the overall poor performance of screenings in terms of reducing morality: the screening test may lack sufficient sensitivity to find diseases early; there may be no markedly effective treatment options for the disease; or treatments are available but the risk-benefit ratio of the whole screening and treatment process is unfavorable.
Whatever the case, the conundrum of whether and when to screen needs to be supported by robust evidence and, toward that end, researchers like Ioannidis believe that randomized controlled trials should be the default.