Antibody tests, even quick finger pricks, are effective COVID-19 screening tools

New findings from Michigan Medicine study reveal that antibody tests are predictive of previous COVID-19 infection and that rapid screening methods – even from finger pricks – are effective testing tools .

The researchers analyzed antibody tests performed on more than 500 subjects in patient care facilities. They found that people with COVID, including those with mild symptoms, produced antibodies.

“For a long time, people were very concerned that people with mild COVID would not have immune responses,” says Charles Schuler, MD, clinical assistant professor of allergy and immunology at Michigan Medicine. “This should give people confidence that the tests available to them are not just random number generators. They are in fact giving them something useful.”

The results also indicate that rapid screenings can predict infection with almost the same accuracy as antibody tests performed in the laboratory. Schuler, who led the research team, says the findings could prove very useful for providers.

“I was actually surprised at the quality of some of these tests, because it’s a very different experience,” says Schuler. “[If you have] a patient in a clinic that doesn’t have a lab on site, we can find out if you’ve ever had COVID and we can do it now and we can do it at low cost. “

The team looked at lateral flow assays, which Schuler describes as modern sunflower tests: a drop of blood or serum is placed on filter paper that changes color to indicate whether antibodies are present.

The researchers then compared three rapid screens taken by finger pricks or blood samples in health care settings with serological tests evaluated in a laboratory. They looked at data from 512 patients, 104 of whom had a history of COVID-19 and a positive PCR test.

Despite a few false positives, two rapid tests agreed with positive lab results 93-97% of the time. Both tests outperformed the third brand, which lost its emergency use clearance from the FDA during the trial.

“I think the FDA has done a good job regulating bad testing off the market,” says Schuler. “These are always accurate in a point-of-care establishment …[so], you have a test that can be performed in different parts of the world and can be performed without the need for a more complex lab environment. “

U.S. vaccination is rising rapidly – nearly 30% of the population has received at least one dose as of March 30, according to the Centers for Disease Control and Prevention. But in places where immunizations are late, Schuler says these point-of-care antibody tests could help determine who has priority.

“It’s important to vaccinate everyone,” he says. “But, if you can direct the vaccines to people, in particular, who may be totally unprotected, something like that would be helpful. I think more data is needed to say that from a policy perspective.”

The study population is small, which raises questions about how the data can be generalized. Almost 90% of those tested are healthcare workers, many of whom provide direct care to patients with COVID-19.

However, Schuler’s team will continue to assess subjects with a new lens. Some recent studies indicate that antibodies can persist and provide protection for several months. Schuler hopes to make this response more concrete.

“This is a down payment on, hopefully, a lot of good future data,” he says. “While antibodies may or may not tell you how immunity occurs, they can alert you to the risk of re-infection. This is the functional clinical significance that we need to know as early as possible.”