COVID-19 virus test results may vary based on time of day: Study

The test sensitivity of SARS-CoV-2, the virus that causes COVID-19, may vary based on the time of the day and the our body's biological clock, according to a study. The research, published in the Journal of Biological Rhythms on Tuesday, found that people were up to two times as likely to have an accurate positive test result if they tested in the middle of the day compared to at night.

The finding supports the hypothesis that COVID-19 acts differently in the body based on our natural circadian rhythm, which has also been implied by studies of other viral and bacterial infections, the researchers said.

Circadian rhythm is our body's natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours.


COVID-19 virus shedding -- when infected cells release virus particles into the blood and mucus -- appears to be more active in the middle of the day due to modulation of the immune system by our biological clock, the researchers said.

"Taking a COVID-19 test at the optimal time of day improves test sensitivity and will help us to be accurate in diagnosing people who may be infected but asymptomatic," said Carl Johnson, a professor at Vanderbilt University in the US.

The results indicate that viral load is lower after 8 p.m, according to the researchers.

If people choose to get tested at that time, there could be a higher chance of a false-negative result, they said.

A difference in COVID-19 viral shedding throughout the day is important information that may inform how we test for and treat the virus, the researchers said.

The peak shedding in the afternoon, when patients are more likely to interact with others or seek medical care, could play a role in increasing the spread of the virus in hospitals and the wider community, they said.

The researchers noted that further research is needed to confirm the diurnal -- meaning active during the day -- nature of SARS-CoV-2.

Experimentally testing patients who are infected with COVID-19 to see if individuals shed the virus differently throughout the day would have important public health implications, Johnson said.

The research can be used to optimise COVID-19 testing and improve test accuracy, he added.

The researchers believe temporal considerations may be leveraged to maximise the effectiveness of intervention strategies and even vaccine strategies.