Coronavirus FAQ: Testing confuses me! When to do it? Is 'negative' always reliable?

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Many of us are returning from spring break travel and holiday celebrations with loved ones just as COVID cases in parts of the United States — and in some other countries — are ticking back up.

Testing for COVID is as critical now as it was in earlier stages of the pandemic in order to understand where cases are rising and so that newly diagnosed patients can seek treatment.

So you may be wondering: When do I need to test? And can I trust a first test result?

First off: If you develop COVID-like symptoms, test as soon as possible.

And let's assume you're going to self-test because you don't have easy access to a facility that offers PCR tests and/or your insurance doesn't cover it and/or you don't want to wait extra time for results rather than an instant read off a do-it-yourself antigen test.

So you take that home test ... and it's negative. Are you in the clear? Maybe, but not definitively. Our experts suggest testing again after a couple of days.

Your body's response to SARS-CoV-2 infection depends on your level of immunity from previous encounters with the virus and from vaccines and boosters.

So it's possible that the negative result is correct, and you simply didn't get infected.

Or you might not have enough "viral load" in the early stages of being infected to test positive. That can happen if you have some degree of immunity from a prior case or a vaccination but you get infected anyway (see: Nancy Pelosi).

That's why experts recommend testing at least twice.

Test number one would come when you first have concerns that you are infected based on symptoms — or if you've been exposed to someone with COVID or were in a higher-risk situation (traveling, karaoke party, Gridiron Club dinner) and then plan to be around an older relative or a child too young to be vaccinated or someone who's immune-compromised?

"If you are going to be around the vulnerable population that can't be protected from the disease – and, unfortunately, we have a lot of people that fall into that category — then you should do everything in your power to try and make sure you don't have the virus," says Omai Garner, director of clinical microbiology in the UCLA Health System.

You might be tempted to test right away to ease your anxiety. But the recommendation from the U.S. Centers for Disease Control and Prevention is to wait five days after a possible exposure.

It takes a little while for the virus to build up in your body. Testing too soon might give you a false negative.

"You can't take a pregnancy test the day after intercourse to see if you're pregnant, right?" says Ida Bergstrom, an internal medicine physician at a medical and travel clinic that conducts testing in Washington, D.C. The rapid test for COVID is "an excellent test — it just has to be used properly and at the right time."

And there's a reason tests come in pairs of two, Garner says. "You need to use them in the pair that they come in, and have multiple days in between, in order to be sure."

And for that second test, waiting a few hours doesn't count because your viral load still might not be high enough to detect. Testing experts suggest an interval of 48 hours before a second test.

Now if you do go for a PCR test, you won't have quite the same concerns. That's because for rapid home tests to turn positive, you need a higher viral load: Those antigen tests don't amplify the sample like PCR tests do.

For those with prior immunity to the virus, "most people feel that a PCR is positive 24 hours sooner than the rapid," says Bergstrom.

If you've developed symptoms after close, significant contact, you might consider getting a PCR even after negative rapid tests.

"If your husband is positive, and you develop symptoms, and you have a negative rapid and then the subsequent day you have a negative rapid — I would still personally do a PCR before I called myself in the clear," Bergstrom says.

Should I contact my doctor if I have a positive test?

YES. There are a few reasons why.

If you are at risk of severe outcomes because of your age or preexisting conditions, you should try to get highly effective antivirals or monoclonal antibodies as soon as you test positive. The faster you can get the treatments, the better they work – but they can only be prescribed after a positive test.

Even if you're not at high risk, you should let your doctor know of your positive test so that they can help you monitor your symptoms and have a more complete record of your health history.

This is a really important step, because you could go on to develop long COVID — even after a mild illness, even if you were previously healthy. Between 10 to 50% of people who recover from COVID have long-term symptoms — a big range because not enough is yet known to narrow it down.

"If your symptoms linger or if there's any question with disability or anything in the future, it's nice that there's a trail," Bergstrom says.

Insurance companies may not cover treatments for long COVID if you don't have documented evidence of a positive test, and you may not be able to apply for disability without it.

It's also a great idea to report your home test results to your local health department, if that's an option, so that they can track local cases. Some states and cities also offer services like deferred rent or mortgage assistance for those who test positive.

Melody Schreiber (@m_scribe) is a journalist and the editor of What We Didn't Expect: Personal Stories About Premature Birth. [Copyright 2022 NPR]