Testing has taken on new urgency in the war against the coronavirus, as elected officials from the mayor to the president try to decide how to keep up the fight while getting Americans back to work. But there are different tests and different populations that need testing, depending on what the goal is. Even simple questions lead to a lot of confusion -- we’ll do our best to explain below.

Where are we in terms of our capacity to test sick New Yorkers for COVID-19?

We’ve dramatically expanded our testing capacity in the last month and half. On Sunday, for example, more than 16,000 test results came back across New York and overall 633,861 have been tested for the virus, according to state statistics. In New Jersey, Governor Phil Murphy says they’re testing about 7,500 people a day. This a big improvement from where we were at the beginning of the outbreak, when all testing was funneled through the Centers for Disease Control and Prevention laboratory in Atlanta, and there were weeks of delays for federal approval of commercial and public health laboratories. Laboratories in our area went from being able to only conduct manual tests, now to fully automated testing, so they can run thousands of samples a day.

With all the expanded capacity, are we at the point where anyone who gets sick can get tested?

No and we’re far from it. The guidance from the health department still prioritizes testing for people who need hospital care, though there has been an increased ability to test for essential healthcare workers and first responders. Northwell Health, for example, now has contracts with the MTA, the state police, the NYPD and the city’s correction department.

But there are also issues with the supply chain, a spokesman confirmed; one main ongoing issue is the supply of nasal swabs needed to take the sample, though the city’s health department also cites a shortage of personal protective gear as another restriction on testing. A spokesman for Northwell said they had about a two-weeks supply of nasal swabs left, though they’d just begun using 3-D printed ones, that could further expand testing capacity in the coming weeks.

At a press conference Tuesday, Governor Andrew Cuomo said he planned to ask for President Donald Trump's increasing the state's testing capacity at his White House meeting that afternoon. He reiterated the need for the federal government to step in to help secure raw materials needed to run more tests so states aren't competing against one another for the same supplies. "When you got to the manufacturers and you say I need you to increase capacity many manufacturers are saying I can't. I can't get enough reagents, I can't get enough swabs...I can't get enough vials, I can't get enough materials for my own test kits. That's the determiner of testing capacity," Cuomo said.

But what about these new testing sites that we’ve heard about? New York City opened several sites on Friday and Monday, and the governor said on Monday he was starting a pilot testing program at several public housing developments. Do they have enough tests?

The city has secured more supplies it needs to conduct these tests, according to a spokeswoman for Mayor Bill de Blasio, and these new city sites are still prioritizing certain at-risk groups. The mayor’s office is partnering with One Medical, which runs five testing sites by appointment for frontline healthcare workers, people with disabilities and city residents who are older than 65 and have pre-existing conditions. Public hospital sites are also testing people over the age of 65 with pre-existing conditions that would put them at risk for serious illness, according to de Blasio’s office. The pilot program at eight public housing developments is slated to open this week and offer free testing to residents there.

However, for weeks now, the city has vacillated between expanding testing and then pulling it back. In mid-March, for example, the city set up testing several sites only to cancel all appointments a day later, when long lines ensued and the shortages of protective gear needed to collect each sample became obvious. And when government efforts stalled, other groups have stepped in, like the non-profit Somos that’s opened testing centers for immigrants in areas with high infection rates. But those groups are competing for the same scarce resources as hospitals and city and state governments are.

There’s a public health consensus that widespread testing is needed in order get a grip on the virus, identify potential hotspots before they flare up, but we’re still a long way off from that. And there’s the added issue of false negatives: a test that comes back negative even if the person has the virus. Some preliminary studies suggest the false negatives rate could be as high as 30 percent of tests taken.

Let’s talk about antibody testing. That can confirm whether I had COVID-19, regardless of whether or not I was tested for the virus -- and even if I had few or no symptoms?

In theory, yes: if you have antibodies, it’s because you were exposed to the novel coronavirus, whether or not you got sick. But the commercially available tests have been unreliable, so there are many false positives and negatives

Dr. Ed Lifschitz, medical director for New Jersey's Communicable Disease Service, says that even if we had enough testing, there are still many questions to be answered. Researchers still haven’t figured out which tests work the best.

“We're still learning a lot about the tests and what they can and can't tell us and which may be better tests than others,” Lifshitz said. “So we're really too early to say, ‘Ah, okay, here's our answer, we're just going to use this test.’”

But if I do have antibodies, that means I’m immune, right? No mask, no gloves, carefree subway rides?

Alas, no. Not by a long shot. Antibodies are a key part of the immune system that fights back against the virus -- but they’re only one part. As Dr. Lifschitz said, a lot more research needs to be done to find out how much immunity people get from different levels of antibodies. Some people might have many, based on their exposure and their body’s response to it, and some might have fewer. And if they do appear to confer immunity, it’s not clear how long that will last -- or how helpful it will be to other strains of SARS-CoV-2, should they emerge.

Listen to our radio story on testing for WNYC here:

The governor says antibody testing is key to opening the state back up, so people can go back to work and school and so on. Why are he and other leaders emphasizing this so much, if much of the testing is unreliable -- and even when it IS reliable, and there aren’t lots of false positives and negatives, we still don’t can’t say “antibodies equals immunity”?

Even with the very provisional information antibody testing provides, it still gives us an epidemiological picture of how far the virus has penetrated into the population -- and that can help officials decide the who and where and when of reopening the economy. We can get a sense of what proportion of society has been exposed and how close we are to “herd immunity.” We don’t know exactly what that percentage will be, but we know that it will be when most people have been exposed -- so that if uninfected people then go out they have a much smaller chance of being exposed. Mind you, we’re nowhere near the capacity to test 100,000 people a day that Cuomo has called for. So the state hopes to be able to make forecasting models -- using a geographically and demographically diverse sample of the state population, starting around 3,000 or so tests a day.

So should I go get an antibody test?

Almost certainly not from a commercial lab, unless you have good reason to believe that lab is using a proper test. That’s difficult to know, so stick with a hospital or blood donation center. Again, this won’t really tell you what level of immunity you have, so the value for the time being is very limited. But as more data rolls in, the antibody level revealed in your test might become more meaningful.

In the meantime, testing positive for antibodies could qualify you to donate plasma that may help some people hospitalized with COVID-19 recover. The New York Blood Center, Mount Sinai Hospital, New York Presbyterian, SUNY Downstate and other hospitals are offering the antibody tests. But there are big caveats: they have limited capacity, most are only offering them to people who tested positive for the virus, and you have to be willing to donate plasma. Due to limited virus testing, many people who are presumed to have contracted COVID-19 were never lab-verified. SUNY Downstate is allowing people to take the antibody tests and donate plasma if they say they had the illness but it was never confirmed. Dr. Michael Augenbraun, who is running this plasma research site, said they will screen prospective donors by asking them a series of questions.

“We want to cast a relatively wide net,” he said. “One of the conundrums we have is that due to the chaos that reigned supreme for a couple of weeks, we effectively stopped testing a lot of people [for the virus] -- and we’d like to get plasma from those people who couldn’t get tests, too.”