Should I do a rapid COVID-19 test or PCR? Public health experts analyze the facts. – Orange County Register

Hour-long coronavirus PCR tests are prompting public officials to push the public to use rapid at-home antigen tests instead, but public health experts warn that the tests Tests lasting 15 minutes are sometimes prone to false negatives.

Massachusetts Governor Charlie Baker said last week: “Rapid testing is, in some ways, a more accurate measure of whether someone is actually transmitting COVID than PCR testing.”

Dr Davidson Hamer, Boston University Professor of Health and Global Health called the governor’s statement “powerful”.

Todd Ellerin, director of infectious diseases at South Shore Health, said while “there is some truth” in the governor’s statement, “it’s complicated.”

We asked experts to analyze the accuracy of rapid at-home antigen tests, PCR tests and come up with when to use one over the other. The answers have been edited slightly for clarity.

How accurate is the rapid antigen test compared to the PCR test?

Ellerin: PCR results, tested in a laboratory, are much more accurate. But if you look at the arc for PCR, it can last longer and often uncover a past infection that may no longer be contagious. When a rapid test comes back positive, that’s probably when a person is most contagious. On the other hand, if you have symptoms and a negative result on a rapid antigen test, it does not mean that you do not have COVID. You need to be cautious and you need to repeat that test several times over a few days. Performing rapid tests several times over a short period of time increases the likelihood of accurate results.

Hamer: With rapid tests, if you’re positive, there’s a good chance a person could be transmitting the virus at that point, but PCR is much more sensitive. It can detect it earlier, but can be positive before a person has a sufficient viral load to transmit and also after a person’s symptoms have cleared and passed the point of transmission. However, rapidity can return negative before the onset of symptoms when a person is still contagious, so PCR remains the best test available today, despite its limitations. .

Are all quick tests created equal?

Ellerin: It’s not clear if all rapid antigen tests are created equal, but they all have an Emergency Use Authorization from the FDA, so minimal accuracy must be demonstrated. But remember, these tests have been shown to be pre-omicrons. Ideally, we’d like these tests to be validated. Until that happens, the chances are high that these tests are missing an infection. It is important that everyone read the instructions carefully.

Hamer: A large number are reviewed and approved by the FDA, under the Emergency Use Authorization. Not all of them are alike, but they are similar in their ability to detect infection in someone with symptoms. A study of about 80 at-home antigen tests showed accuracy to be close to 100% in cases of patients with high viral loads, but it declined fairly quickly. That means patients who are asymptomatic or have a low viral load can still transmit, but their infection could be missed by rapid testing.

When should I do a rapid coronavirus test versus a PCR test?

Ellerin: The good news about rapid testing is that you get results quickly, so if you don’t have access to PCR, you can still tell. However, there is concern about missing an infection, especially when it comes to omicrons and any variations that emerge afterward. The best time to use PCR is when you can get results back quickly.

Hamer: If someone develops symptoms and they want answers quickly, antigen is the way to go, especially if access to PCR testing is not available. Antigen tests are more likely to be accurate if you have symptoms and were exposed within the last 2 to 5 days. PCR tests are great for population-scale surveillance like the pooled testing that happens in schools, where the key is to try to detect infections early. PCR is really useful if there is a short turnaround time of less than 24 hours and a low cost.

Should I do a rapid antigen test before attending events?

Ellerin: In an ideal world, yes. But for it to work, people would test it a few days before and again just before that. Unfortunately, there isn’t enough access to rapid antigen tests right now for that to happen.

Hamer: I’m not sure if this can be used as an effective screening tool for going into events. If someone is infected but has no symptoms, the chances of an antigen test finding that someone is infectious is low.