An Illinois company that has played an outsized role in coronavirus testing said Wednesday it has created an antibody test and will ship nearly 1 million units to U.S. customers before the end of the week, adding its muscle to a piece of the response that is deemed critical but still a work in progress.

Abbott Laboratories, whose rapid diagnostic for COVID-19 is being used by the White House, said it will ship about 4 million antibody tests in April and will be able to produce about 20 million per month by June.

“It’s a great test,” President Trump said, highlighting it at his daily briefing as part of ongoing efforts to combat the virus.

The company joins at least 90 others that have developed a “serology test” to determine whether someone has had the disease — many people might not know — and developed antibodies that protect them from future infection.

The White House, New York Gov. Andrew Cuomo and others say the tests will help them figure out who has developed natural defenses and can return to work amid a pandemic that has infected more than 600,000 Americans, killing nearly 28,000 of them.

Yet state leaders and federal regulators say they’re still trying to pinpoint the most accurate tests and ways to increase production.

The Food and Drug Administration has approved tests from three companies — cellex, Chembio and Ortho — for what’s known as emergency use. The authorization puts a third-party stamp of confidence on those tests, though additional companies are marketing tests without an FDA review of their data.

That approach was allowed under FDA guidance from March, although companies must validate their tests and notify federal regulators if they go to market.

“I am concerned that some of the antibody tests that are in the market that haven’t gone through the FDA scientific review may not be as accurate as we’d like them to be,” FDA Commissioner Stephen Hahn told NBC’s “Meet the Press” on Sunday. “I can assure the American people that what we’re doing is using data and science to look at those tests to make sure they’re valid, they’re accurate, and they’re reproducible.”

The FDA said it’s working with the Centers for Disease Control and Prevention and the National Institutes of Health to evaluate how well the tests already on the market perform.

“This project is intended to complement and inform FDA review as needed. This validation project is ongoing and we hope to have additional information to share in the future,” the agency told The Washington Times on Wednesday.

Scott Becker, CEO of the Association of Public Health Laboratories, said he’s glad federal agencies launched the effort “so that we can get a sense of the quality of these tests.”

He would like all companies to strive for an emergency use authorization, because there is a give and take with regulators over the quality of their data in that process.

In Louisiana, a top official said the state is looking into a “large number” of serology tests but won’t dive in until it gets firmer signals from the federal government. The state wants to be confident the tests are picking up COVID-19 alone.

“If I had the [common] cold this year or last year, is my coronavirus serology test going to show up positive? We don’t want that,” said Alex Billioux, assistant secretary for the state Office of Public Health.

“Right now, that’s the main hindrance why you aren’t seeing us buy up these coronavirus tests,” he said. “The sensitivity and specificity may be within where we want them, but our concern is we don’t want to be telling people, ‘You’ve had the virus before, you may be able to behave differently,’ if indeed what it’s picking up is that I had a cold earlier in the year.”

Gov. John Bel Edwards said a Louisiana State University lab is developing its own test.

New York Gov. Andrew Cuomo, meanwhile, said his state’s Department of Health developed its own antibody test and wants to conduct 2,000 tests per day with a finger prick.

“That test is going to be very important and it’s in our control. We don’t need a private lab, we don’t need anyone else,” he said Wednesday.

CDC Director Dr. Robert Redfield said ramping up antibody testing is key to try to determine how many asymptomatic people spread the virus and whether health workers are protected, “particularly as the cases come back next fall.”

“So that’s ongoing,” he told ABC’s “Good Morning America.” “I think these health care workers are extraordinary and I think we will show that a significant percentage of health care workers in high-risk areas did, in fact, get infected in the line of their work.”

Mr. Cuomo said New York will prioritize the antibody testing for health care workers, first responders and essential workers. He is trying to open up his economy as the number of hospitalizations and intensive care unit (ICU) admissions stabilizes in his hard-hit state.

Mr. Cuomo did report 752 new coronavirus-related deaths in New York, pushing the state total above 11,000.

Other states haven’t seen a big wave of cases, so it might be premature to begin serology testing.

“We’re just exploring antibody tests right now. Want to be careful about how we deploy that,” Mikelle Moore, the chief community health officer for Intermountain Healthcare in Salt Lake City told Mr. Trump at the White House this week. “And because we don’t have many people who have been exposed to the disease in our communities, it might not be time yet.”

For now, companies reached by The Washington Times said they are shipping their antibody tests directly to labs and health systems.

Abbott shipped its first batch to large U.S. health systems that have lab equipment compatible with its other products, mainly at hospitals and commercial reference labs.

The antibody checker is the third test rolled out by Abbott during the pandemic, after its high-capacity m2000 testing machines and its ID NOW rapid test, which can spit out results in minutes and is being used by the White House to test people who come in close contact with Mr. Trump or Vice President Mike Pence.

The company said its newest test identifies the IgG antibody, a protein the body makes in the latter stages of infection and may remain for months or even years after a person has recovered.

Abbott Labs said it is shipping tests under earlier FDA guidance that allows it to market its product but that it will seek emergency use authorization from the agency.

Chembio, meanwhile, said it distributing its product to “all routine channels” — hospitals, clinics and other medical facilities that offer antibody testing — but is also working with “all local and state government agencies in order to provide this valuable tool to the medical community.”

The federal government, which faced criticism for stumbles in diagnostics that detect COVID-19 on the front end, says it is working to rapidly evaluate more serology tests as they come online.

In a statement, the Health and Human Services Department said: “To date, three serological assays have been given an EUA by the FDA. We expect the availability of serological assays to rapidly scale by May, so that by this time, millions of serological tests will be available.”