Viewpoint: What physicians may miss in reading lab results

Physicians often misunderstand test results, particularly in grasping how false positives work, meaning they may make crucial medical decisions based on incorrect assumptions, a chief of hospital epidemiology writes in The Washington Post.

Four insights from the op-ed, written by Daniel Morgan, MD, chief of hospital epidemiology at the Baltimore VA Medical Center:

1. The first issue physicians face in interpreting tests is misunderstanding probability, Dr. Morgan says. In a 2014 study, most physicians could not assess the positive predictive value, or the probability patients with a positive screening test actually have the disease. The most common error in the study was a large overestimation of positive predictive value, an error that could significantly affect patients' diagnosis and treatment, the study authors said.

2. Additionally, many physicians may fail to recognize the tests they rely on are highly prone to error. In a study Dr. Morgan published in 2017 with colleagues to evaluate the necessity of patients' tests, nearly 90 percent of patients had at least one unnecessary test. Overall, the study found about one-third of all the tests were unneeded.

"When patients receive tests that aren't needed, there is a reasonable chance that doctors are using the results to make choices about treatment; by definition, these choices have a higher danger of being flawed," Dr. Morgan writes.

3. In a 2016 paper, Dr. Morgan and colleagues interviewed more than 100 physicians about their understanding of the risks and benefits of 10 common medical tests or treatments. They found nearly 80 percent of the subjects overestimated the benefits.

"Strangely, the doctors themselves acknowledged this, with two-thirds rating themselves as not confident in their understanding of tests and probability," Dr. Morgan writes. "Eight out of 10 said they rarely, if ever, talked to patients about the probability of test results being accurate."

4. Although there is no simple solution to this issue, one step is for physicians to recognize the gaps in understanding and improve knowledge of what each test can accurately tell them, Dr. Morgan said. "Medical schools and professional associations can also do a much better job of educating doctors to understand how risk and probability work."

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