Think you have COVID? Wait two days to test for better accuracy

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If you feel COVID-19 symptoms, you might be tempted to test right away.

However, new research suggests that waiting two days could give you a more accurate result.

This finding comes from a study published in the journal Science Advances by researchers at the University of Colorado Boulder.

Their new mathematical model also offers insights into testing for other viruses like the flu and RSV (Respiratory Syncytial Virus).

For COVID-19, the best time to test is two days after symptoms start.

Testing too early can lead to false negatives, meaning the test says you’re not infected when you actually are. In fact, if you test right away, you might get a false negative up to 92% of the time. Waiting two days reduces this to about 70%.

If you can take a second test on the third day, you increase your chances of detecting the virus.

For the flu and RSV, it’s different. These viruses multiply quickly, so testing as soon as you feel symptoms is the best approach. The rapid tests for these viruses are more likely to be accurate right away.

The researchers, Casey Middleton and Professor Daniel Larremore, developed this model to help with the challenges of rapid testing. They looked at how different factors, like the behavior of various COVID-19 variants and patient responses, affect test accuracy.

“COVID-19 has changed over time, and each variant behaves differently,” said Larremore. “This means the timing of when to test can vary.”

Their model showed that because many people have some immunity from previous exposure, their bodies react faster to the virus, causing symptoms before there is enough virus present to be detected by a test.

This creates a dilemma: testing immediately for all three viruses (COVID-19, flu, RSV) can give accurate results for flu and RSV but might be too early for COVID-19. Waiting a few days improves the chances of detecting COVID-19 but might be too late for flu and RSV.

While the false negative rate for COVID-19 tests might seem high, these tests are designed to catch people with high viral loads who are most likely to spread the virus. Identifying even a third of infections can significantly reduce transmission.

The study also suggests that a “test to exit” strategy, where people test before ending isolation, could be more effective and convenient than the previous five-day isolation rule. This approach can help release people who are no longer infectious while keeping those who still have high levels of the virus isolated.

This research could help improve rapid tests and guide better advice for clinicians. It also has the potential to provide quick, data-driven recommendations if another pandemic occurs.

“If done correctly, the next generation of rapid tests could be very impactful,” said Larremore.

In summary, if you suspect you have COVID-19, wait two days before testing for the most accurate results. For flu and RSV, test as soon as you feel symptoms. This approach will help you get the best use out of your at-home tests and keep everyone safer.