How to Get the Most Accurate Results from an At-Home COVID-19 Test
[ad_1]
While experts advise people who think they may have COVID-19 to test on day 1 of symptoms, a new study suggests that for people using home (rapid) kits, testing again on day 4 may yield the most accurate results.
For the study, scientists examined data on 348 adults newly diagnosed with COVID-19 based on PCR (polymerase chain reaction) testing. PCR tests are administered by medical professionals and are considered the gold standard because they’re extremely sensitive and can detect even very low levels of coronavirus. All study participants provided detailed information on when their symptoms started and any recent COVID-19 testing history.
Researchers then administered rapid tests to see if and when results would match those from the positive PCR tests.
The scientists found that the rapid tests were most likely to match PCR results four days after symptoms started, when viral loads, or the amount of virus in the body, typically will peak, according to study findings published in Clinical Infectious Diseases.
“This means that the sensitivity of home COVID tests would be expected to be highest around the fourth day of symptoms, even though many symptomatic people might test positive on home tests before that,” says senior study author Nira Pollock, MD, an associate medical director of the infectious diseases diagnostic laboratory at Boston Children’s Hospital and an associate professor of pathology at Harvard Medical School.
You Should Still Test When Symptoms Start
The study results don’t mean that people should put off testing if they have COVID-19 symptoms like a sore throat, runny or stuffy nose, coughing, sneezing, fever, chills, shortness of breath, muscle aches, fatigue, or headaches, Dr. Pollock says.
“People should continue to test as soon as they have symptoms, because if they test positive, that information is very important for making decisions about isolation and treatment,” Pollock says. “The key is that people need to know that one test is not enough.”
The Centers for Disease Control and Prevention (CDC) recommends that people with COVID-19 symptoms who test negative take a second test 48 hours later. This advice shouldn’t change based on the study results, Pollock says. But the study findings do suggest that people who are negative after two tests should consider doing one more on the fourth or fifth day after symptoms start.
Do a Follow-Up COVID-19 Test if the First Is Negative
One limitation of the study is that the rapid tests used by researchers to assess the optimal testing day based on viral loads are used only in medical settings, making it possible that results may differ with the rapid tests widely available for home use, says Matt Binnicker, PhD, director of clinical virology at Mayo Clinic in Rochester, Minnesota.
Still, the study results confirm the importance of doing another test if the first one is negative, says Dr. Binnicker, who wasn’t involved in the new study. “The CDC guidelines are still relevant and performing a test when symptoms first appear is a good idea,” Binnicker says. “However, a negative initial test should be interpreted with caution and follow-up testing on day 4 appears to be warranted.”
People should also take precautions to prevent spreading COVID-19 if they have symptoms and only one negative test, Pollock says. “Even if the person doesn’t have COVID, they likely have another infection that they could transmit to other people,” Pollock adds. “It is always a good idea to stay home when ill. Ideally, one would mask around other people until repeat test(s) are negative.”
George Rutherford, MD, a professor and head of the division infectious disease and global epidemiology at the University of California in San Francisco, agrees that multiple at-home COVID tests are needed if the first one is negative, and that people should take steps to avoid spreading infections when they have symptoms.
But Dr. Rutherford, who wasn’t involved in the new study, also stresses that there’s another very effective way to protect against COVID-19.
“I don’t want to lose the bottom line advice, which is to get vaccinated,” Rutherford says.
[ad_2]
