The Affordable Care Act (Obamacare) requires health plans that started on or after Sept. 23, 2010, to cover colonoscopy as a screening test (although older plans may not), and Medicare covers the cost of this test every two years for people 50 and older at high risk and every 10 years for people at average risk. (Colonoscopy can actually prevent cancer, not just detect it; if a polyp is found in which cancer could develop, it can be removed during the screening.)

Doctors themselves often directly or indirectly encourage ill-advised screening tests. As two California doctors, Dr. Deborah Grady and Dr. Rita F. Redberg, who are concerned about overuse of screening mammography, recently noted, “Payment systems in the United States typically reward ordering tests and procedures over taking the time to talk to patients about risks and benefits.”

They also pointed out that doctors often fear litigation if they fail to perform or order a test and the patient later turns out to have a cancer that might have been cured had it been detected sooner.

And doctors often believe at least as strongly as their patients do in the benefits of screening tests. For example, if you are a woman 55 or older, both the American Cancer Society and the guidelines issued by the United States Preventive Services Task Force recommend mammogram screening every two years (the task force recommends starting at age 50). But most doctors who endorse screening think it should be done annually, even for women 75 and older, according to a recent report in JAMA Internal Medicine.

Although among young and midlife adults, the main challenge for doctors can be convincing them of the benefits of screening, among people in my age group and beyond, the difficult task more often involves advising patients that it’s time to forgo screening.

“Clinicians are frequently uncomfortable stopping cancer screening,” a medical team at Johns Hopkins University School of Medicine and School of Public Health reported in June. As a result, “Older adults with limited life expectancy are frequently screened for cancer even though it exposes them to risks of screening with minimal benefits,” they reported in JAMA Internal Medicine.

Practice guidelines for physicians called Choosing Wisely advise not recommending cancer screening to patients with a limited life expectancy. However, as the Hopkins team found in interviewing 40 older adults, many people believe that doctors cannot accurately predict a person’s life expectancy and don’t want to consider how long they may live when making screening decisions.