When Is Evidence Enough to Justify Widespread Screening?

Kenneth W. Lin, MD, MPH


November 13, 2017

Editorial Collaboration

Medscape &

Hello, everyone. I'm Dr Kenny Lin, a family physician at Georgetown University Medical Center in Washington, DC, and I blog at Common Sense Family Doctor.

Last year, I wrote an editorial in American Family Physician that argued against routinely screening for chronic hepatitis C in adults born between 1945 and 1965 with no known risk factors.[1] Although this position contradicts recommendations from the US Preventive Services Task Force and the Centers for Disease Control and Prevention, I continue to believe that the outcomes of a birth cohort screening strategy are uncertain, given the absence of randomized trials with patient-oriented outcomes, the high cost of antiviral drugs, and data showing that most patients with chronic hepatitis C do not progress to liver failure or develop liver cancer even decades after being infected.[2]

In June, a Cochrane systematic review of direct-acting antiviral drugs for chronic hepatitis C concluded that there was insufficient evidence to assess their effect on health-related quality of life, morbidity, or mortality.[3] This conclusion surprised many experts and provoked negative reactions from leading hepatologists. In an editorial that appeared in the Annals of Internal Medicine, Dr Anna S. Lok and colleagues strongly rebutted the Cochrane group's findings and their recommendation to conduct randomized trials before expanding hepatitis C treatment beyond persons with symptoms of liver disease.[4] "Although randomized controlled trials are important," they argued, "they cannot be justified in situations where the evidence of benefit is so obvious, and physicians have to do what is right for patients."

Lok and colleagues' words reminded me of a much-cited spoof article that claimed to be a systematic review of randomized controlled trials of parachutes to prevent injury and death from jumping out of airplanes.[5] Of course, there are not and never will be such trials because the evidence of benefit is so obvious. But a subspecialist's conclusions about what medical interventions are equivalent to parachutes and, therefore, require no further study may not be generalizable to primary care.

For example, it has long been accepted that one quarter to one third of persons with diabetes in the United States remain undiagnosed, which has been a strong impetus for guidelines that recommend widespread screening. However, a recent cross-sectional study[6] based on national survey data with confirmatory testing (rather than a single fasting glucose or glycated hemoglobin measurement) suggested that only 1 in 10 persons with diabetes is actually undiagnosed—still a significant percentage, to be sure, but a much smaller fraction than previously thought.

Not only will fewer people with diabetes be detected by screening, research proof of the long-assumed cardiovascular benefit of early detection of diabetes, which I questioned in a previous Medscape commentary, continues to be elusive. The second major trial to compare mortality rates and cardiovascular events between screened and nonscreened groups in nearly 2 million Danish adults aged 40-69 years found no differences in these outcomes after a median follow-up of 9.5 years.[7]

All of this isn't to say that researchers won't eventually find convincing evidence that diabetes screening and/or hepatitis C treatment improve patient-oriented outcomes. But it does highlight a need for clinicians to be skeptical about claims of "obvious" or certain benefit for interventions that we provide in primary care. If there's one thing I've learned from years of practicing family medicine, it is that parachutes are few and far between.

This has been Dr Kenny Lin for Medscape Family Medicine. Thank you for listening.


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