Here's how accurate at-home rapid Covid tests are and when to use them for free.

You can obtain a handful of free at-home Covid tests through the Biden administration's new website, covidtests.gov.

The website, which launched officially on Wednesday following a soft launch on Tuesday afternoon, enables each U.S. household to order four rapid antigen Covid-19 tests. According to the website, orders are expected to ship within seven to 12 days.

The surge in demand for at-home tests has been driven by the record-setting pace of infections and hospitalizations caused by the omicron variant.

This guide can assist in determining the accuracy of at-home rapid tests and when to use them.

How accurate are at-home rapid antigen tests?

Antigens are detected by at-home tests through rubbing a nasal swab inside nostrils and exposing it to chemicals. The results appear in about 15 minutes.

The Centers for Disease Control and Prevention reports that at-home antigen tests like BinaxNow are approximately 85% accurate in detecting positive cases. This implies that at-home tests miss about 15% of positive cases, which may seem like a significant number when millions of people are tested daily.

PCR tests are considered the gold standard in Covid testing, but rapid tests are quickly catching up in terms of accuracy, according to Gigi Kwik Gronvall, a senior scholar at the Johns Hopkins Center for Health Security.

PCR tests can detect genetic material or fragments from specific organisms or viruses, such as Covid-19, to determine if you are currently infected or if virus fragments are still present in your system after you have recovered. However, the downside is that these tests take time, with results only being available in a laboratory setting, meaning even the quickest turnarounds can still take at least 24 to 48 hours.

While at-home tests aren't completely accurate, they are still valuable due to their convenience. Dr. James Crawford, senior vice president of Laboratory Services at Northwell Health and professor at the Feinstein Institutes for Medical Research, emphasizes their importance in the "national strategy for reducing the spread of this virus."

A preprint study led by Johns Hopkins researchers found that rapid antigen tests and PCR tests have similar accuracy levels for children. The study is awaiting peer review.

When should you take an at-home test instead of a PCR test?

If you suspect you have Covid symptoms, take a rapid antigen test. If you're asymptomatic but worried about potential virus exposure, take a PCR test.

Gronvall states that rapid antigen tests are effective in determining if an individual is currently contagious and should self-isolate.

If you have Covid, you'll be the most contagious when you first experience symptoms, according to Gronvall. This makes rapid tests more likely to confirm or deny your infection, as the more viral load you have, the more likely a rapid test is to catch it.

The "viral load" is highest when the tests were originally approved by the FDA, according to Crawford.

Gronvall recommends watching a how-to video before using at-home tests for the first time, as it might be helpful for those who are not familiar with the process.

If your rapid Covid test returns negative but you experience symptoms similar to the virus, the CDC advises that you may have a false negative result. The agency suggests isolating yourself from others and contacting your healthcare provider for further guidance. Additionally, you may want to consider getting a PCR test as an additional measure.

PCR tests are more useful than rapid antigen tests for people who are asymptomatic, according to Crawford. This is because PCR tests are more sensitive, making them better suited for screening purposes, especially if you have been exposed to Covid but are feeling fine or simply want to be screened for peace of mind.

According to Crawford, there is a greater likelihood of an at-home test yielding a negative result in an infected asymptomatic individual compared to a laboratory-based PCR test.

Multiple at-home rapid Covid tests, including Abbott's BinaxNow tests, the Ellume Covid-19 Home Test, and the Quidel QuickVue At-Home Covid-19 Test, are available for purchase without a prescription, in addition to the free at-home tests provided by the Biden administration.

According to online websites, prices fall between approximately $14 and $35.

The CDC has updated its guidance on testing negative for Covid-19 even if you are experiencing symptoms.

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