More and more Utahns are expressing interest in getting tested for COVID-19 antibodies, but health care experts, including federal authorities, advise against using the tests to determine how much protection they have against the deadly virus.

“Immunity is incredibly complex. Unfortunately, folks want a simple yes/no answer. And like most things, the real answer is, ‘It depends,’” said Han Kim, a professor of public health at Westminster College in Salt Lake City, adding “the risk of misinterpretation is too high” with antibody tests.

Antibodies are only one aspect of the immune response, and it’s not yet known what levels are needed to fight off future disease, Kim said. That makes it “hard to predict whether you are immune to COVID in the future based on these tests, and that’s ultimately what people want to know.”

So, he said, there’s no reason to seek out the test “unless you want to give away money.”

The U.S. Food and Drug Administration issued a “safety communication” in May spelling out that results from “antibody tests should not be used to evaluate immunity or protection from COVID-19 at any time, and especially after the person received a COVID-19 vaccination.”

A positive result from testing for antibodies — proteins made by the immune system to fight infections — doesn’t mean someone is immune from COVID-19, the FDA says, warning that interpreting the results that way could lead to people taking fewer precautions even though they still may become infected and spread the virus.

But that hasn’t stopped Utahns from asking their doctors about the blood test, especially as the highly contagious delta variant of the virus is driving a surge in cases around the country, including instances of breakthrough infections in those who are vaccinated that are raising questions about booster shots.

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“Absolutely” there’s increased interest from patients in antibody tests, said Dr. Brandon Webb, an Intermountain Healthcare infectious diseases physician. “Not surprisingly, health care providers are finding themselves having conversations about the benefits and limitations of antibody testing much more frequently.”

Webb said he believes that’s because “it’s top of mind for the public to know” how protected they are against COVID-19, whether they’ve previously had the virus or are vaccinated. But he said the tests “actually could create some false sense of security.”

The accuracy of the tests for COVID-19 antibodies varies widely, Webb said, and there’s no agreement yet on which are the most reliable and even what the results mean, so “in general, antibody testing is still not recommended.”

He said, for example, someone who caught the virus earlier, when a different strain was circulating, might test positive for antibodies “which is terrific, but that doesn’t necessarily mean that individual is fully protected against the delta variant. That entirely depends on the individual’s health, age, immune status and other factors.”

Dr. Julio Delgado, ARUP Laboratories executive vice president, said antibody tests, including those from the nonprofit University of Utah facility, are used to identify outbreaks, convalescent plasma donors and the disease in children and others who never got tested for COVID-19 but are dealing with long-term effects.

Children color pictures for a vaccination bulletin board.
Hope and Lana Ruth Thompson color pictures for the COVID-19 bulletin board in front of them while waiting for their mother to get vaccinated at the former Provo High School in Provo on Friday, Aug. 6, 2021. The folded up bleachers in the gymnasium serve as a bulletin board to post notes about why folks have chosen to get a COVID-19 vaccination. | Jeffrey D. Allred, Deseret News

Antibody tests have been used to study whether someone who is immunocompromised due to an organ transplant, cancer treatment or other medical condition benefits from an extra dose of COVID-19 vaccine, Delgado said

For most Utahns, Delgado said, he doesn’t see “any rational or logical reason that is supported by science now that people would go on their own and try to get themselves an order for an antibody test, or even worse, to try to get one of those over-the-counter tests, because those are even more inaccurate.”

What he termed the curiosity surrounding antibody testing may be a result of a new study of breakthrough cases in Israel showing a correlation between those who were infected and low antibody levels, suggesting the delta variant replicates so quickly, for some there wasn’t time for the vaccine to kick in.

The findings are “a little bit worrisome” and already starting to be discussed on social media, Delgado said. “I anticipate there’s going to be a lot of interest. ... People are going to start to say, ‘Wait a second. I want to know how much of the antibodies that I have now that we’re surrounded by delta.’”

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In just the last week, he said, he’s heard from University of Utah Health colleagues who are getting requests from their healthy patients who want to know their antibody level. Delgado said his answer is that there is not yet a threshold for what that level should be.

That may come as pharmaceutical companies attempt to make a case for booster shots, he said. Pfizer, maker of a two-dose vaccine, has announced it will seek emergency approval from the FDA to provide a third dose as added protection against the delta variant.

Webb said the issues with antibody tests are the focus of the booster shot debate.

“That’s what the FDA is laboring over right now, is how to make those recommendations when testing and test results and levels are not standardized,” he said. “So linking those recommendations to some type of antibody test level requires the tests themselves be more standardized and the interpretation of the results be a little more concrete.”

For now, patients who want an antibody test are told “we wouldn’t necessarily know what to do with the results,” Webb said, offering instead specific advice for those at a higher risk of contracting COVID-19 because of their age or medical condition, vaccinated or not.

“Rather than have their antibody levels checked,” he said, “I think the more practical and more effective counsel is simply for them to double-down on the precautions that they’re taking while the delta variant is surging — limiting gatherings, wearing masks in indoor settings and distancing when possible.”