How Accurate Are At-Home Covid Tests? Here’s a Quick Guide

In case you missed. Bottom line: A good tool to help you determine if your an infection risk to others(have a high viral load). If your in early stages of a COVID infection (low viral load), you can throw a false positive.

How Accurate Are At-Home Covid Tests? Here’s a Quick Guide

When used correctly, many rapid antigen tests are good at detecting people carrying high levels of the virus.

By Emily Anthes, NY Times

Dec. 17, 2021

In the early months of the pandemic, getting a coronavirus test typically required visiting a health care center, a laboratory or a dedicated testing site, a process that sometimes involved long lines and waiting a week or more to get the results.

Americans can now take rapid antigen tests from the comfort of their own homes. Many of these tests are available without a prescription and return results in just 15 minutes.

Demand for the tests has surged in recent months, as the highly infectious Delta variant has spread and schools and offices have reopened; now the even more infectious Omicron variant has arrived. “All the manufacturers are ramping up production, but right now they can be hard to find,” said Gigi Gronvall, a testing expert at Johns Hopkins University.

Although rapid antigen tests have their limitations, they are an important public health tool, experts said, particularly if you know how to use them.

“Having that information and being able to make better decisions is very powerful,” said Mara Aspinall, an expert in biomedical diagnostics at Arizona State University who is also on the board of directors of OraSure, which makes rapid Covid tests. “And the ability to do this on a while-you-wait basis is something that we couldn’t do a year ago.”

What kinds of tests are available?

A handful of rapid antigen tests are available without a prescription, including the Abbott BinaxNOW, the Ellume Covid-19 Home Test and the Quidel QuickVue At-Home Covid-19 Test. Prices start at about $7 per test, although President Biden has announced plans to reduce prices by roughly one-third.

All three detect small viral proteins, called antigens. The tests require rubbing a shallow nasal swab inside your nostrils and then exposing the swab to a few drops of chemicals. They provide results in about 15 minutes.

The tests themselves are fairly straightforward, but each one involves a slightly different procedure, which should be followed to the letter. “If you’re doing at-home tests, you must read the instructions and follow them meticulously,” said Dr. Patrick Godbey, a former president of the College of American Pathologists.

Ms. Aspinall concurred. “This is not the time for creativity,” she said.

How accurate are rapid antigen tests?

Polymerase chain reaction tests, which have typically been considered the gold standard for detecting the virus, are typically performed in a laboratory and involve making many copies of the virus’s genetic material. That process helps P.C.R. tests to detect even minute traces of the virus.

Rapid antigen tests, which do not amplify the virus, are less sensitive than P.C.R. tests. If you take one during the earliest phase of an infection, before the virus has replicated widely, the test could return a false negative.

Some of the at-home rapid antigen tests have an overall sensitivity of roughly 85 percent, which means that they are catching roughly 85 percent of people who are infected with the virus and missing 15 percent. In some studies, their real-world performance has been even lower.

But the tests are more sensitive in people with symptoms than without and are most sensitive during the first week of symptoms, studies have found.