Which COVID-19 test will give the answers you need?

People lined up for a variety of COVID-19 tests in Hackensack. Each test measures something different. A nose swab or saliva test can tell if you’re currently infected, if there’s genetic material from inside the coronavirus in your body, making someone a possible disease vector even if they don’t have symptoms.

“We’re able to identify those who are asymptomatic but have the virus, get them the health care help that they need, and also do the contact tracing along with that, so that’s really what this is all about,” said Bergen County Executive Jim Tedesco.

The Bergen County mobile test site offers 500 to 600 of the nasal and saliva tests daily, but only about 100 blood draws. Blood samples take more time and require a special technician. The blood tests check for antibodies and can tell if a person’s already had COVID-19 and recovered. They can’t really measure your level of immunity. The CityMD urgent care network recently had to clarify that after incorrectly telling 15,000 New York and New Jersey clients they were immune.

“The serology tests are not meant to be an immunity passport. We don’t know whether this is useful information for whether or not a person can return to work safely, without the risk of possible reinfection,” said state epidemilogist Dr. Tina Tan.

Now, a company called Quidel is offering a brand-new COVID-19 diagnostic test which just got FDA approval. It detects antigens, or different proteins, that attach to the outer covering of the coronavirus. The good news is that it’s cheap and blazing fast.

“If the test works, it’s very fast. It can get a result in, I don’t know, 10 minutes, something like that,” said Dr. Martin Blaser, director of the Center for Advanced Biotechnology and Medicine at Rutgers.

But Blaser says Quidel’s antigen test only positively identifies the virus in 85% of patients. It returns a lot of false negatives telling patients that they’re infection-free when they’re not.

“You do a test to be sure, that’s why you do tests. And if the test isn’t 100% then you have a grey area. And the bigger the grey area, the less value the test has,” Blaser said. “This antigen test is still, I would say, the first generation of those kinds of tests.”

State health officials reserved judgement on the antigen test.

“We’re learning more as more of these tests come online. At this point, as to whether we’d be recommending purchasing or we’d say wide scale that we’d be going that way rather than a rapid tests, rather than all these other tests, at this point, no we do not yet have a conclusion as to what our recommendation will be,” said Dr. Ed Lifshitz, medical director of the communicable disease service at the New Jersey Department of Health.

Bottom line: think of the tests as a snapshot — telling you if you have the virus or if you’ve been exposed to it. None of them can guarantee immunity. For that we need a vaccine.