COVID-19 testing may be more accurate in the afternoon – Community News
Covid-19

COVID-19 testing may be more accurate in the afternoon

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Does the time of day affect COVID-19 test results? Ian Montgomery/EyeEm/Getty Images
  • A new study finds that the accuracy of COVID-19 reverse transcription polymerase chain reaction (RT-PCR) testing follows a daily pattern.
  • The highest number of accurate positive results occurs with afternoon tests, while evening tests increase the number of false positives.
  • The study also suggests that mid-afternoon is the time of day when both symptomatic and asymptomatic individuals are most likely to transmit the SARS-CoV-2 virus to others.

When a COVID-19 test returns a false positive — meaning a person doesn’t have SARS-CoV-2 infection, but the test is positive — it unnecessarily disrupts that person’s life.

However, a false negative — when someone has an infection, but the test is negative — is more harmful. This is because treatment is inappropriately delayed and the individual may infect others if they continue to participate in their normal daily activities.

A new study from Vanderbilt University in Nashville, TN, suggests that the time of day a person takes an RT-PCR COVID-19 test can affect the chance of an inaccurate result.

The study found that the participants were up to twice as likely to get an accurate positive result if they were tested in the middle of the day and not at night.

Principal investigator Dr. Carl Johnson tells Vanderbilt University Research News, “Taking a COVID-19 test at the optimal time of day improves test sensitivity and will help us be accurate in diagnosing people who may be infected but asymptomatic.”

The research results suggest that the human body’s daily clock — the circadian rhythm — influences the behavior of the SARS-CoV-2 virus during each 24-hour cycle. Other research related to viral and bacterial infections has supported this hypothesis.

The study appears in the Diary of Biological Rhythms.

The study authors analyzed a dataset of 86,342 clinical trials conducted at approximately 130 clinics between March and August 2020. The clinics were affiliated with a regional health care network in the southeastern United States. Both symptomatic and asymptomatic subjects were tested.

The highest number of positive results was from tests taken in the mid-afternoon, around 2 p.m.

This indicates that it is at this time of day that viral shedding, that is, the release of infected particles into the blood and mucus, is most active.

dr. Johnson told: Medical news today in an email: “The reason we imply shedding is that the highest amount of free viral particles in the mucus, [blood, or both] should occur immediately after the viral particles are burst from the host cells (ie, are shed) and before they infect new host cells.”

During shedding, a person with SARS-CoV-2 infection — even if they are asymptomatic — is most likely to transmit the virus when they talk, exhale, and eat around other people.

The data analyzed also indicates that a person’s viral load decreases after 8 p.m. This means that a positive result from a test taken at that time of day is more likely to be a false positive.

“Because the circadian clock regulates the immune system, immunity functions better or worse at different times of the day. This is a likely reason why [SARS-CoV-2] viral shedding may be rhythmic. Perhaps the virus is shedding itself at a time of day when the immune system is least able to deal with it. But this is just a prediction at this stage – no hard evidence at this point.”

– dr. Carl Johnson

The researchers adjusted the results for age, gender, race, test location, month, day of the week and other factors — “we eliminated the possible confounders we could think of,” said Dr. johnson.

The analysis revealed a 1.7-fold variation in the probability of a positive result over a 24-hour period.

The study authors hope its insights will lead to more accurate test results when looking at the circadian cycle of SARS-CoV-2.

They also cite possible policy implications of their findings if additional testing confirms their insights.

First, understanding the 1.7-fold variation in test sensitivity over the course of a day can help clinics “optimize the time for test collection, interpretation of results, and patient guidance.”

Second, knowing what time of day the shedding is most active can help those providing care create patient visit schedules that minimize the risk of spreading the virus.

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