How Accurate COVID Home Tests Are as Joe Biden Announces Free Rapid Kits

The Biden administration announced on Tuesday that 500 million free rapid COVID home tests would be mailed to U.S. households starting from next month, as the country battles its latest wave of the virus.

Government-funded free rapid testing has been part of various countries' COVID responses for months. In Canada, some provinces provide free COVID tests to businesses. In Germany, free COVID tests have been available since March, despite a brief pause in the autumn.

The U.K. has also been a leader in terms of free universal testing. In England specifically, people can currently order a pack of seven rapid lateral flow tests per day via the government website.

In the U.K., they're used to identify COVID cases in people who don't have symptoms, with the aim of reducing the pre-symptomatic spread. It's advised that people take a test before going to social events where there is a high risk of COVID infection, if they are going to visit someone who would have a high risk of severe illness if they were to get COVID, or if they've been in contact with someone with the coronavirus.

Following Biden's announcement yesterday, U.S. citizens will also soon get free access to a number of rapid tests.

Rapid lateral flow tests aren't as accurate as polymerase chain reaction (PCR) tests at detecting the coronavirus. The benefit of lateral flow tests, though, is that they don't need to be sent to a lab for evaluation and provide a result in 10 to 30 minutes.

Part of the reason PCR tests are better at detecting COVID is that they can detect very small amounts of the COVID virus present in someone's body that lateral flows may miss. This is because PCRs repeatedly amplify tell-tale signs of COVID in a given sample to see if it is there, while lateral flows do not.

Sensitivity of the Tests

Reports on the sensitivity of lateral flow tests—their ability to detect a positive case—vary. It depends on whether the person being tested has symptoms or not, and if the sensitivity is being measured relative to a PCR.

One asymptomatic pilot study conducted in the U.K. city of Liverpool estimated that the sensitivity of a lateral flow test was around 40 percent. A Danish study put it at 69.7 percent. A Centers for Disease Control and Prevention (CDC) study found that the sensitivity of rapid tests relative to PCR was 36 percent for asymptomatic people and 64 percent for symptomatic people.

A study by researchers at various universities, including University College London (UCL) and the Harvard T.H. Chan School of Public Health states: "These diverging figures have provoked debate about the sensitivity of the LFTs and concerns have been raised about their utility in the context of testing asymptomatic individuals."

The same study also criticized comparing LFTs to PCRs, with the latter being used as a "gold standard" since they work in different ways and don't necessarily identify the same cases. "This is like comparing apples and oranges," said lead author Professor Irene Petersen in a UCL statement.

That study suggested LFTs could be more than 80 percent effective at detecting any level of COVID infection.

Test Results Shouldn't Be Ignored

In any case, if a lateral flow test does come up positive, experts have stressed that they should not be ignored. "It's very likely you have COVID if you get a positive lateral flow test," Petersen told Bloomberg, which reported a false positive rate of less than 1 in a 1,000.

This is because a false positive lateral flow test result is rarer than a false negative. A negative test result doesn't necessarily mean you don't have COVID, but a positive test result more than likely means you do have it, according to the vaccine alliance Gavi.

Gavi's website states: "This is because the specificity of LFTs [lateral flow tests]—their ability to accurately diagnose uninfected individuals—is higher, and therefore false positives are highly unlikely."

Lateral flow test
A person holds up a positive lateral flow test in Penarth, Wales, on December 15, 2021. Lateral flow tests can be used to detect COVID rapidly. Matthew Horwood/Getty