It’s a thought that’s passed through the minds of many: Did I have the coronavirus before the pandemic even started? Others wonder if they’ve…
It’s a thought that’s passed through the minds of many: Did I have the coronavirus before the pandemic even started?
Others wonder if they’ve carried the disease but remained asymptomatic, while some reflect on whether or not contracting and recovering from the virus offers them immunity.
All of these questions are what make COVID-19 antibody testing — blood screens that can detect who has previously been infected — so enticing.
Antibodies, which are detectable about five to seven days after symptoms begin, are proteins in the blood that are produced in response to an infection.
Having COVID-19 antibodies can help medical professionals make definitive coronavirus diagnoses, Massachusetts General Hospital said in a news release, adding that antibody testing, or serology testing, paves the way to understanding the body’s immune response post-infection, the spread of the virus through asymptomatic patients, and the length of time that person can expect to be protected.
“We know immunity occurs to some degree. We see it, and we can actually measure antibodies in people’s bloodstreams,” Dr. Edward Ryan, MGH director of Global Infectious Diseases, said in a statement. However, “We’re still in the very early stages of knowing immune responses to COVID-19, as not all antibodies are created the same.”
But there are caveats — the CDC recently posted new guidance on its website warning that many antibody tests have shown false positive results among the general population.
“In a population where the prevalence is 5%, a test with 90% sensitivity and 95% specificity will yield a positive predictive value of 49%. In other words, less than half of those testing positive will truly have antibodies,” the CDC said in its updated guidelines.
And in more high-prevalence settings like nursing homes, there’s a higher chance for false negative results, according to the CDC.
Results are not yet accurate enough to refer to when making important policy decisions either, the CDC said.
“Serologic test results should not be used to make decisions about grouping persons residing in or being admitted to congregate settings, such as schools, dormitories, or correctional facilities,” the health institute wrote.
