For months, the White House’s strategy for keeping President Trump and his inner circle safe has been to screen all White House visitors with a rapid test.

But one product they use, Abbott’s ID Now, was never intended for that purpose and is known to deliver incorrect results. In issuing an emergency use authorization, the Food and Drug Administration said the test was only to be used by a health care provider “within the first seven days of symptoms.”

The ID Now has several qualities in its favor: It’s portable, doesn’t need skilled technicians to operate and delivers results in 15 minutes. Used to evaluate someone with symptoms, the test can quickly and easily diagnose Covid-19, the disease caused by the coronavirus.

But in people who are infected but not yet showing symptoms, the test is much less accurate, missing as many as one in three cases.