Antibody tests not always accurate, but still an important tool

The antibody test that was thought to be key to the state’s reopening, but it has reliability issues, leaving health care providers and state leaders questioning what the data really tells us about community spread and safely reopening the state.

“While some individuals are interested in antibody testing, at this time there is still a lot that remains unknown about the value of that testing. A positive result on an antibody test should not be viewed as definitive evidence of immunity, or even past infection with COVID-19. It also cannot tell us if you currently have the virus. So I encourage residents to get a diagnostic test as this is the most valuable tool we have now, right now, to contain the spread of the virus,” said New Jersey Department of Health Commissioner Judith Persichilli at a press briefing on May 29.

Sick in early March with a viral upper respiratory infection, I took the antibody test. Negative or positive, can the results be trusted?

“It’s the nature of medical testing in general, and the general community doesn’t understand that,” said Dr. Adam Jarrett, chief medical officer for Holy Name Medical Center. “Every test has a sensitivity and a specificity, which is a calculated false positive or false negative rate, so it is inherent in medical testing. It is why, when you do testing, you don’t just look at the test. You look at the clinical situation, the patient’s history, the patient’s physical examination, and then you use the test and you put it all together and make the diagnosis.”

He says the sensitivity rate, or percentage chance that the test could be inaccurate, is actually similar to the rate of the coronavirus test at around 25% wrong. But he says there’s still value in getting the community tested for antibodies.

“If we don’t do that, then we have this puzzle that has missing pieces and we don’t fully understand it. So we need to do the testing, but we need to understand the inherent problems with the testing,” Jarrett said. “It takes a long time for medicine to understand a new disease. And that’s what this is, it’s a new disease.”

Jarrett says the results shouldn’t guide behavior, because as Persichilli said, the antibodies don’t necessarily mean immunity.

“No one knows at this point how long these antibodies stay in your system,” he said. “But you can’t really change your behavior based on it at this point. We still need to follow careful social distancing. And as we open up society, we need to do that slowly, two, three weeks at a time, make changes and see if there’s an impact, and not rely on the antibody test by itself.”

Holy Name plans to begin antibody testing of all COVID positive patients starting three months after their illness so they can begin tracking the data and the effectiveness of tests.