But even if it were possible to increase the sensitivity to 90 percent, the magnitude of risk remains substantial as the number of people tested grows, Sampathkumar argued in a paper published in Mayo Clinic Proceedings.

“In California, estimates say the rate of COVID-19 infection may exceed 50 percent by mid-May 2020,” she said.

With 40 million people, “even if only one percent of the population was tested, 20,000 false-negative results would be expected.”

This makes it critical for clinicians to base their diagnosis on more than just the test: They must also examine a patient’s symptoms, their potential exposure history, imaging and other lab work.