Important points
- A recent study suggests the best time to get an at-home COVID-19 test may be the fourth day after symptoms appear.
- Despite the study’s findings, experts say people should follow the CDC’s current guidelines, which say people with symptoms should get tested immediately.
- People who do not have symptoms but have been in contact with someone infected with COVID-19 should be tested at least five full days after the exposure.
People who are suspected of having an infection are generally tested for the new coronavirus infection (COVID-19) on the first day they develop symptoms. However, in a study published in clinical infections For those using rapid at-home tests, this suggests the best time to test may be the fourth day after symptoms appear.
Researchers analyzed data on 348 adults newly diagnosed with COVID-19 based on PCR tests. These tests are gold standard It is highly sensitive and can detect even small amounts of coronavirus, so accuracy is required. This is the type of coronavirus test you would normally get in a doctor’s office and requires laboratory analysis to get results.
All study participants shared information about when their symptoms started and any recent COVID-19 tests they had taken. The researchers then used in part what is called a single-molecule array test to examine antigen concentrations to determine when rapid tests would be most sensitive among this group of people. performed an analysis.
The findings suggest that rapid test results taken four days after the onset of symptoms are most likely to match PCR test results. Research shows that this is the time when the amount of virus in the body, known as the viral load, typically reaches its highest point.
“This means that the sensitivity of at-home coronavirus tests is low even though many people with symptoms of SARS-CoV-2 infection may test positive with an at-home test before that. “This means that the highest levels are expected to occur around the fourth day after emergence,” said the study’s lead author. Nila Pollock, MDThe associate medical director of Boston Children’s Hospital’s Infectious Disease Diagnostic Laboratory told Berrywell in an email.
What makes a test accurate?
He said the accuracy of the test depends on its sensitivity, specificity and the amount of disease it can detect, including the amount of coronavirus. Dr. Charles BaileyMedical Director of Infection Prevention at Providence St. Joseph Hospital and Providence Mission Hospital in Orange County, California.
The current study “suggests that the timing of peak viral loads has changed in recent years,” Bailey told Berrywell in an email.
This may be because the researchers were testing an adult population with strong immune systems. 91% had a history of vaccination, natural infection, or both.
Sensitivity refers to a test’s ability to accurately detect infection, while specificity refers to a test’s ability to rule out infection in people who have not tested positive for coronavirus. Dr. Heba Mostafa, MBBChHe is an associate professor of pathology at the Johns Hopkins University School of Medicine and director of the Institute for Molecular Virology at Johns Hopkins Hospital, he told Berrywell via email. Tests with low specificity are more likely to give false positives.
“Based on publications, the sensitivity is expected to increase at day 4, and the specificity is high regardless of the day the test is performed,” Mostafa said. “But based on all the information we have collected so far, [rapid] Antigen tests are lower than molecular tests [PCR] test. A symptomatic person whose antigen test is negative should take her second test 48 hours after the first test. This approach is expected to increase sensitivity. ”
Don’t change your testing habits yet
Researchers say this small study should not be the basis for changing testing habits.people need to stick to it Current guidelines Recommended by the Centers for Disease Control and Prevention (CDC) if you have symptoms of COVID-19. This means testing right away.
People who test negative for coronavirus through a rapid test will need to take another test 48 hours later.
Pollock said that while his research has identified peak testing times, there is no need to delay testing if you experience symptoms such as a headache, sore throat, cough, stuffy nose, fever or chills. Ta. The sooner you test positive, the sooner you can make decisions about isolation and treatment to keep yourself and others safe.
“Importantly, we need people to understand that one test is not enough. If the first test is negative, they must be tested again 48 hours later, as recommended by the FDA and CDC. “There is,” Pollock said. “Our study suggests that if the second test is negative, another test may be needed on the fourth or even fifth day after symptoms appear. ”
Are CDC testing guidelines likely to change?
Established policies and guidelines typically don’t change based on a single study, Bailey said. Additionally, the study had a relatively small sample size and used PCR cycle threshold data to extrapolate hypothetical results for rapid antigen tests, which typically would not lead to policy changes, he said.
“In my view, changes to the guidance should be driven by appropriate representation of all relevant patient cohorts (e.g. age, gender, vaccination status, immunocompetence, etc.) and the inclusion or implementation of antigen testing. “We will need a larger sample.” Bailey.
Still, he said studies like this one, especially since this study was conducted from “the backyard of the CDC in Atlanta,” are a step toward updating guidelines in the future if needed.
CDC spokesperson Jason MacDonald told Berrywell that the agency will update guidance as necessary in line with ongoing data monitoring.
“Agency staff and scientists are actively reviewing our COVID-19 guidance to ensure it continues to reflect the current state of the virus and the data,” McDonald said.
When should I get tested if I don’t have symptoms?
MacDonald said if you have been in contact with someone infected with COVID-19 but have no symptoms, wait at least five full days after the exposure before getting tested.
He reiterated that people who test negative with a rapid home test must test again within 48 hours. If both tests are negative, consider giving her a total of 3 additional tests 48 hours later. You can order your free home test below. COVIDTest.gov.
what this means for you
Recent research suggests rapid tests are most likely to detect coronavirus infection four days after symptoms appear, but experts say continue testing as soon as symptoms appear. I think it should be done.
The information in this article is current as of the date of publication, so new information may be available at the time you read this article. For the latest information on coronavirus disease (COVID-19), visit our coronavirus news page.