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Infectious disease doctor, state epidemiologist, CDC cast doubt on accuracy of COVID-19 antibody tests

Posted at 7:31 PM, May 27, 2020
and last updated 2020-05-27 21:31:47-04

New guidance from the Centers for Disease Control and Prevention (CDC) suggest COVID-19 antibody tests often are inaccurate.

“For example, in a population where the prevalence is 5%, a test with 90% sensitivity and 95% specificity will yield a positive predictive value of 49%,” the CDC reported. This means, in some populations, the accuracy of the antibody test will be accurate only about half the time.

This isn’t unexpected, Utah Epidemiologist Dr. Angela Dunn, said. The CDC is referencing one of the more accurate tests where a vile of blood is taken, Dunn said.

“The other one that has been really popular, especially in the Salt Lake area is the finger prick test. And those take a really small amount of blood and actually studies have found they are wrong more often than they are right,” she said.

The Utah Health Department currently gets all the results of the COVID-19 antibody tests done statewide. So far, about 15,000 Utahans have been tested, only about 750 have come back positive, Dunn said. Right now, each of those individuals who test positive are contacted by the health department.

“We are reviewing those plans now given this new information that they are indeed wrong 50 percent of the time. Is it worth public health resources to actually reach out to these individuals or not,” Dunn said.

There is really no reason an individual consumer needs to pay to get a COVID-19 antibody test, Dr. Daniel Leung, Associate Professor of Infectious Disease at the University of Utah and Infectious Disease Physician for U of U Health. Antibody testing should really be used to inform public health policy decisions because on a larger scale the testing can be more accurate, Dr. Leung said.

“What I am is saying is that we would want to use this on a population level and on a population level, there are certain statistical methods we can use to adjust for that test performance,” he said.

There is still so much we don’t know, Dr. Leung said. More studies need to be done, but this is the best guidance based on the information we have at the time. When COVID-19 antibody testing first started gaining popularity, many wondered if the test could determine immunity to the virus.

“Even if you truly have the antibody, we still don’t know if that translates to immunity or protection,” Dr. Leung said.

“I really wish that we had a test right now that we could determine who was immune and who wasn’t. That will come. Right now, there is evidence that there might be an opportunity for people to get re-infected. So, being infected with Covid-19 multiple times is a possibility,” Dr. Dunn said.

People should not use antibody test results for personal decision making, Dr. Dunn cautioned.

“From a public health standpoint, we are using this information on a population basis, but not recommending it for individual decision making,” she said.

FOX 13 News asked Governor Gary Herbert what, if, any role Covid-19 antibody testing results are having on policy and or decision making in Utah.

“The answer is none. The state is at the very front end of a field study with the University of Utah that makes use of antibody testing to estimate how far and wide the coronavirus may have spread throughout our community. We are a long way off from seeing results from that testing, and much further away from learning from infectious disease specialists on what those possible results might teach us,” he said in a statement.

For more information on the CDC’s guidelines on Covid-19 antibody testing, click here.