Elon Musk said he tested positive and negative for Covid-19—here's what you need to know about the different tests

Elon Musk said he tested positive and negative for Covid-19—here’s what you need to know about the different tests

Published Fri, Nov 13 2020

Cory Stieg

On Friday, Elon Musk said that in one day he took four Covid-19 tests — called rapid antigen tests — and received two negative and two positive results. He also tweeted that he took two PCR tests at separate labs and is waiting for the results.

Musk, who has been dismissive about Covid-19 and its severity, tweeted that something “extremely bogus” was going on.

The truth is, no test is 100% accurate all of the time. But Musk’s experience still begs questions: What are antigen and PCR tests? How accurate are they? And who should take them?

Here’s what you need to know.

Rapid antigen tests

How it works: Rapid antigen tests require a nasal sample that can be collected at home or by a healthcare provider. They work by identifying specific proteins that are found on the surface of the novel coronavirus when someone is infected with Covid-19.

Although these types of tests are cheap to manufacture (they can cost $25-$100 out of pocket) and can deliver test results in a matter of minutes, they are not as reliable as polymerase chain reaction, or PCR, tests (more on that below).

Accuracy: The “sensitivity” rate, or how effective a test is in identifying people with antigens, is between 84-98%. According to the Food and Drug Administration, “positive results from antigen tests are highly accurate, but there is a higher chance of false negatives.” For this reason, it’s recommended that people get both a rapid antigen test as well as a PCR test (within two days) to confirm on a molecular level whether someone has Covid-19 or not.

In particular, Musk said he took rapid antigen tests from BD, the global medical company, Becton, Dickson and Company. While Musk’s very small sample of four tests clearly only got the result right 50% of the time, in BD clinical studies, the tests achieved an 84% sensitivity rate. Musk said he also followed up with a PCR test. (BD did not immediately respond to CNBC Make It’s request for comment.)

Who should take them: Rapid antigen tests work best when someone is tested in the early stages of the virus, when they have a high viral load. These tests are useful for [screening in congregate . . .

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