Health Care

Urgent care centers champion antibody tests, as state officials urge caution

coronavirus testing lab
Valarie Devlin and Alan Finn, microbiologists at the Vermont Department of Health Laboratory, test specimens for the Covid-19 virus in March. State officials have urged caution about a different type of test that screens for antibodies. File photo by Mike Dougherty/VTDigger

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Charles Keating thought he might have had Covid-19 in March. His mother-in-law tested positive for the virus around that time, and soon afterward, he lost his sense of taste and smell.

In early June, the 34-year-old Bolton resident got confirmation that his hunch was right. Keating, his wife Samantha, and both his in-laws all tested positive for Covid antibodies. He had his blood drawn at ClearChoiceMD Urgent Care in South Burlington, and the test result, which arrived the next morning, showed that he had the antibodies that fight coronavirus. 

“It gave me a little peace of mind,” Keating said. But, he added, he wasn’t putting too much stock in the results. “I still will do my part and wear my mask,” he said. 

Keating is one of a small, but growing, number of Vermonters who have sought out the test. While surrounding states, including New York and Massachusetts, have rolled out widespread antibody screenings, Vermont officials have been loath to offer them broadly.

Health Commissioner Mark Levine, a fixture at Gov. Phil Scott’s three-times-a-week coronavirus updates, has repeatedly discouraged the use of the tests. His fear is that they are unreliable and the results can be misleading. So far, most Vermont hospitals have not offered to test people. Meanwhile, some urgent care centers have started offering them without restrictions; more than half of the 1,350 state residents who’ve been screened for Covid-19 antibodies have had their test done at one of the four ClearChoice MD Urgent Care centers in Vermont.

Reluctance from health and state officials and enthusiasm from the urgent care centers has led to mixed messages about the tests.

“There seems to be some differences among the various state health departments, not only New Hampshire and Vermont but across the nation, about the value of the antibody tests,” said ClearChoice MD CEO and Founder Dr. Marc Hampers.

He advocated providing the test to whoever wants it.

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“My personal feeling is that this is important information because the only way we’re really going to get back to normal is to gather as many data points as we possibly can to determine which people develop antibodies,” he said. His company had provided at least 10,000 tests in New Hampshire alone, he added. 

Screening for antibodies 

An antibody test, also called a serology test, screens for antibodies in the bloodstream. Antibodies are triggered as part of the body’s defense mechanism against diseases, including Covid-19. 

The antibody test is different than the nose swab, or PCR, test. That diagnostic test determines whether a person is actively infected with the virus. The serology test measures whether coronavirus antibodies are present in the blood, indicating that the body has already fought off the virus. 

Two kinds of antibodies appear in the bloodstream after exposure to Covid-19. IgM antibodies appear after about seven days and disappear after a few weeks. A second type, IgG antibodies, appear after 14 days and are likely to provide longer-term immunity — though how long remains unclear.

The Food and Drug Administration issued emergency approval for the tests in early April, but the initial enthusiasm around the tests diminished as more research emerged; The New York Times reported that only three of the original 14 antibody tests delivered accurate results.


Since then, the tests have improved; some are 99% accurate.

However, that high rate of accuracy of the antibody tests can be deceiving, Levine explained during a press conference on Monday. The test results are less reliable when fewer people across the state have been infected. Depending on how many people in Vermont have been exposed to Covid-19, the false positive rate for antibody tests may be 50% — or higher, he said.

FAQ: Are serology tests accurate?

It’s all in the numbers. If 100 Vermonters tested positive for the coronavirus from the swab test, 99 of those people, on average, would also test positive later in the antibodies test. That scenario would produce one false negative.

The problem is when the 100 are random and have not necessarily been exposed to Covid-19. In Vermont, officials estimate the infection rate is closer to 5%.

That means if 100 people are tested, five people should test positive for the presence of Covid-19 antibodies. But if the 99% accuracy rate produces an incorrect result 1/100 times, that means that six people will test positive, not five. One out of six positive tests will be inaccurate, an error rate of 18%.

That’s why Levine has said the 99% accuracy rate doesn’t guarantee the tests provide meaningful results.The lower the infection rate, the less accurate the figures will be from widespread antibody testing. The antibody tests are more valuable in populations where infection is prevalent — the “sensitivity rate” would be higher regarding who had the disease and had some immunity.

Such estimates are conservative. The actual error rate of antibody tests may be higher than 50%, according to Levine.

See VTDigger’s Covid-19 Knowledge Base.

There’s also no scientific consensus about what having Covid-19 antibodies actually means. Experts are unsure whether people can get Covid-19 a second time or how much immunity the antibodies provide.

Varied approaches

Conflicting scientific claims has led to inconsistent guidance and varied approaches to antibody testing in Vermont.

Copley Hospital in Morrisville was among the first wave of hospitals nationally to start offering the tests to area health care workers.

Since April, 274 workers have been tested for antibodies, according to a report of the results sent to the Department of Health last week. Thirteen tested positive for IgM antibodies, with 14 inconclusive tests. The test results didn’t align with those who had previously tested positive for active Covid-19 infection, which raised questions about the reliability of the tests, wrote Copley’s Chief Medical Officer Don Dupuis, author of the report. 

Copley also tested for longer-lasting IgG antibodies. None of the 211 people who got the test were positive, though three of the results were inconclusive. That test also required more vetting to know whether or not it was accurate, Dupuis said.

CEO Joe Woodin stood by the value of the antibody tests for research. “You have strong IgG [antibodies], what a relief it would be,” he said, noting that his goal was peace of mind for his employees. “We’re not saying don’t wear a mask.” 

Soon after Copley started offering antibody tests in April, Levine said publicly that it was too early for the state to offer them on a widespread basis. 

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Instead, Levine convened a working group to study the idea. The group initially said the state didn’t have enough scientific research to support serology testing. But after its second meeting in May, the group issued a list of three scenarios in which an antibody test would be worthwhile, said Clayton Wilburn, a pathologist and medical director for clinical chemistry from the UVM Medical Center.

Officials recommended the antibody test for those who wanted to donate plasma with Covid-19 antibodies to the Red Cross, perhaps providing sufferers some help. Tests were also approved if the results could help a doctor decide treatment options. The tests were also recommended for kids who show symptoms of multisystem inflammatory syndrome in children (MIS-C), an array of autoimmune symptoms that could be triggered by the coronavirus.

The narrow set of criteria haven’t allowed for many tests. As of Monday, Wilburn had received 27 requests from doctors around the state and approved just eight. Four of those eligible patients had been tested, all of which had come back negative. 

Providing testing to anyone who wants is irresponsible, Wilburn argued, because those who test positive for the presence of the antibodies assume they have full immunity. That could lead them to return to work prematurely, or stop wearing a mask, exposing others to the virus. 

“A lot of folks are already dead set that [the presence of antibodies will] give them immunity,” he said. The science doesn’t yet back that claim, he said. “Right now all it tells you is whether you’ve been exposed.”

While state medical officials and most hospitals have been reluctant to recommend widespread testing, others are endorsing the test wholeheartedly.

Some private urgent care centers are offering testing with minimal screening. In Vermont, ClearChoice has run nearly 700 tests. Concentra, another urgent care facility, is also offering testing for asymptomatic workers whose employers want them to return to work. 

Keating, the Bolton resident who got the test last week, signed up online, and scheduled an appointment within 24 hours. His blood was drawn and he got his positive test results the following morning.

He was glad to have the results, he said, but added that he wouldn’t stop social distancing or wearing a mask. “We still have to be careful no matter what until we know more,” he said.

Patricia Crocker, an occupational therapist who lives in Essex Junction, also got the test hoping to get answers. Crocker had suffered a bad cough, congestion, and fatigue in March, she said, and signed up for the antibody test earlier this month. Ultimately, she tested negative for antibodies. 

She said she knew the results may not be accurate, but just had to assume they were — “what else can you do?” she said.

An opportunity for more information?

Most of the antibody tests have been negative, which reflects the small number of Covid-19 cases in Vermont, according to Levine. About 6%, or 84 of the total 1,350 tests, have come back positive, he said.

Hampers, CEO of ClearChoice, contended the results are valuable, especially for those who get both types of Covid-19 tests — the nose-swab test, which measures active infection, and the antibody test, which screens for past infection. The accuracy rate is much higher for those who have already tested positive with a PCR test, he said; after all, those people already know they have the virus antibodies.

“Dr. Levine assumes that we must choose between the two tests,” Hampers said in an email. “But rather, ClearChoiceMD endeavors to provide caregivers with information from a combination of the tests that is often much more useful than a single test.”

Collecting as much information as possible about the virus — even if that data is imperfect — is valuable, Hampers argued. Early on in the spread of the virus, when Covid-19 tests were limited, there was debate about who should get the nose swab diagnostic test. Then, as tests became more available, the Centers for Disease Control and Prevention “made it clear that when the [testing] supply is adequate, there’s no such thing as too much testing,” Hampers said.

Information from serology tests can help in contract tracing and also determine who had the virus and but didn’t have symptoms. “This is all important information,” Hampers said.

It’s also the model that has been adopted around the region, he added. New Hampshire started widespread antibody testing in early May and has conducted more than 16,000 tests. The state’s Governor Chris Sununu contracted with ClearChoice MD to provide tests for those who are underinsured or uninsured. Conducting antibody tests would provide a clearer picture of where the virus had spread, Sununu said at the time. 

Hampers estimated ClearChoice had provided 10,000 tests in New Hampshire alone.

Massachusetts has tested 60,000 people for antibodies. Leaders in Maine have warned of possible inaccuracies in the results of antibody tests, but have still run more than 6,000 tests. 

Even Levine and other skeptics say that the antibody test could prove useful down the line. It could eventually help provide some guidance on who can get back to work with some immunity. Widespread antibody testing could be helpful if any vaccine is in short supply and could be provided only to those who test negative for the antibodies, Levine said.

Catherine Antley, a pathologist who also works for Copley Hospital, said she’s looked into buying the equipment so she could run serology tests in her South Burlington lab. But she hasn’t made the jump; Antley isn’t confident enough in the technology to make a big financial investment. 

But she remains optimistic that antibody testing will become increasingly common. “As a nation, we’re slowly separating the wheat from the chaff and seeing which tests can come to the surface and will be useful and reliable on a long-term basis,” she said.

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Katie Jickling

About Katie

Katie Jickling covers health care for VTDigger. She previously reported on Burlington city politics for Seven Days. She has freelanced and interned for half a dozen news organizations, including Vermont Public Radio, the Valley News, Northern Woodlands, Eating Well magazine and the Herald of Randolph. She is a graduate of Hamilton College and a native of Brookfield.

Email: [email protected]

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