New study shows the time of day you're tested could affect COVID test results

Covid testing
Posted at 2:09 PM, Nov 14, 2021

NASHVILLE, Tenn. (WTVF) — Could the time of day you get tested for COVID impact the accuracy of the test result? According to a new Vanderbilt University Medical Center study, the answer may be yes.

The team studied the results of 86,342 COVID tests performed from March through August of 20-20.

The study looked at whether circadian regulation of the immune system or cycles of viral shedding in people with COVID infections could vary depending on the time of day, thus influencing test results.

Turns out, the study showed early afternoon- specifically at 2:06 p.m.- was when a test was least likely to produce a false negative.

"The [COVID] test is pretty darn accurate," said Dr. Carl Johnson, a professor at the Department of Biological Sciences. "However, if you're COVID-positive, the test is more likely to pick that up when your viral load in your blood or mucus is going to be higher than lower."

The study also found the positivity rate for younger people was much higher than for older people.

“The daily pattern we found for these test results could be down to a host of patient factors that vary over the day, factors which are already known to pose various clinical implications. These factors involve not only the immune system but the autonomic nervous system, body temperature, fasting/feeding cycles, hormones and so on,” said Dr. Candace McNaughton, associate professor of Medicine at the University of Toronto (and formerly at VUMC).

At the time of the study, those in the sample set were unvaccinated