Covid-19 antibody tests rolling out at West Marin Medical Center


The West Marin Medical Center is now testing for Covid-19 antibodies—and is aiming to test as many people as possible. Antibody testing, which detects a body’s immune response to the novel coronavirus, is a promising yet unproven tool for public health officials in their pursuit of an end to the pandemic. The center’s testing of patients began on Monday, with Quest Diagnostics running the blood samples in its laboratories and returning the results within two days. “They are legitimate,” doctor Colin Hamblin wrote of the tests in an email. “I’m not sure we know what to do exactly with the results yet, because we don’t know what level of antibodies is needed for protection against re-infection, but at least we’d know if someone has had [Covid-19] in the past.” Patients can call the center, and before going in they will have a remote consultation. The tests are covered by most insurances, along with Medicare and Medi-Cal; the center will work with uninsured patients to cover costs. “Everyone in West Marin should get it done,” Dr. Hamblin said. For health officials, antibody testing can help reveal how close a region is to herd immunity, which occurs when enough of a population is immune to a disease so that it can no longer spread. The only way to reach herd immunity is through vaccination or infection; since a widely available vaccine is still not yet in sight, the strategy for defeating the novel coronavirus is to slow its spread to the point that people are getting infected, but not in numbers that would overwhelm the health care system. Dr. Matt Willis, the public health officer for Marin, estimated that roughly 5 percent of the county has some level of immunity, including himself. To achieve herd immunity, more than 90 percent of people need to be immune, he said. The unanswered question of how long a person stays immune looms over this approach, which is why Dr. Willis said the county is still at least a month away from promoting widespread antibody testing for residents. “Does [a positive result] mean I have lifelong immunity, or just a couple of weeks?” he asked. “We presume there is at least some degree of protection that’s offered for some time, and knowing that level will be very important.” The antibody tests detect Immunoglobulin G, or IgG, antibodies, which protect against disease in the long term. If the test is conducted too soon after active infection, the body may not have produced enough IgG antibodies to be detected, leading to a false negative result. (The test can also sometimes detect antibodies from other types of coronaviruses, causing a false positive result.) Quest Diagnostics did not specify exactly how accurate the test is, presumably because more data is needed. In Bolinas, over 1,800 residents, essential workers and first responders were tested last week for both active infection and antibodies. Researchers from the University of California, San Francisco have chosen to run two different antibody tests on the blood samples, with results expected in a couple of weeks.