As Hawaii carefully considers reopening the economy, the first laboratory-based coronavirus antibody tests will begin Thursday to ascertain how many people have actually been infected in the islands.

Clinical Labs of Hawaii will start offering blood tests to detect the most common type of antibody — immunoglobulin G, or IgG — that develops about two weeks after COVID-19 infection. The presence of antibodies — proteins produced in the blood by the immune system to protect against viruses — generally means a person has immunity.

Antibody testing may be a game-changer in lifting restrictions and opening the state back up for business, said Lt. Gov. Josh Green. Clinical Labs of Hawaii will be drawing a blood sample for its testing, but antibody testing can be done with a simple finger-prick.

Green is pushing for the tests to be used on passengers arriving in the islands. Current restrictions require most interisland and out-of-state travelers to self-quarantine for 14 days through May 31. The state and counties also imposed stay-at-home orders on residents and have asked tourists to stay away.

If you have the antibody, “it’s a sign you’ve beaten COVID-19 and have some immunity,” Green said, adding that typically people with antibodies have modest immunity for 18 months to three years. “Having an antibody test is going to be valuable as we set our policy on who can and can’t come to Hawaii.”

To be sure, the Centers for Disease Control and Prevention has said people with the antibodies could still be infectious. It is also unclear whether the antibodies will protect people from getting reinfected by COVID-19 or whether enough people will have the antibodies to make opening the economy safe.

“None of these things in and of themselves are solutions, but they give us more information on how vulnerable we are and already how much immunity we have in the background,” Green added.

The antibody tests are for people who were already exposed to the new coronavirus, including those without symptoms, while the diagnostic tests currently being used detect the virus and active infection.

Health care providers will be able to order the tests, which cost about $50. Clinical Labs said the tests are authorized by the U.S. Food and Drug Administration for emergency use during the public health crisis.

“It is a game-changer. There’s probably some asymptomatic folks … who were infected and just don’t know. I’m hoping people get tested, and those people hopefully will never get infected again,” said Dr. Owen Chan, medical director of Clinical Labs. “Hopefully, it stays with you for rest of your life. We still don’t know how our immune systems will work with this particular virus. No one really knows because this virus just came onto the world stage literally months ago. We presume your immunity will be there, but that’s only a presumption because we don’t have the experience yet. Time will tell.”

A spokeswoman for the state’s other major commercial lab, Diagnostic Laboratory Services Inc., said its COVID-19 antibody testing will be up and running soon.

“There are the tools now for us to at least put together a plan to admit people to the state as tourists or returning residents safely,” said Dr. James Ireland, a community physician. “Nothing is perfect. Nothing is gonna be 100%, but we can greatly reduce the risk by using these tests.”

Michele Cox, chief operating officer of Clinical Labs, said the company is able to conduct 1,000 tests per day in-state with results in 24 hours and can send a couple thousand more to a sister laboratory on the mainland. The company plans to ramp up testing over the next few weeks to 5,000 tests per day.

“It will also tell us how long and how widespread the virus has already been here. Now that the testing market is opening up and there’s more availability and capacity, we can increase who we can test. Now is the perfect time as the government looks to open up the businesses,” she said. “It’ll make a big difference. It’ll give some folks peace of mind.”

Hawaii’s tally of coronavirus cases rose by two, to 609, on Tuesday, including the first known confirmed case of a Lanai resident who contracted the virus while hospitalized on Maui. The state’s coronavirus death toll stands at 16.

Since the start of the outbreak, 505 patients have recovered — nearly 83% of those infected in Hawaii. A total of 28,577 COVID-19 diagnostic tests — which involve inserting long swabs into the back of the nose to retrieve virus particles — were conducted by state and clinical laboratories, with 2.1% testing positive.

“Now there’s very little (diagnostic) testing that’s necessary because it’s burning out,” Green said, adding that the state must now look at ways to deal with hot spots, outbreaks and, most important, large numbers of travelers in Hawaii. “There’s going to be a lot of potential discrimination against tourists if we start getting outbreaks of COVID-19 after being cleared as a state. It (antibody testing) is going to be valuable for us if we want to assure ourselves we’re not going to see large surges of COVID-19. It’ll tell us who’s safe and able to fight off the disease going forward. That’s very helpful.”

Clarification: Antibody testing can be done by a finger-prick blood test, however the antibody testing by Clinical Labs of Hawaii starting Thursday will be done by drawing a blood sample. An earlier version of this story did not specify how the testing would be done.