Newly Launched Coronavirus Blood Test Identifies Past Exposure

A pair of new serological tests can detect novel coronavirus antibodies — evidence in persons tested that they have previously been infected by SARS-CoV-2, the viral cause of COVID-19 — even if they never experienced tell-tale symptoms. The tests, developed by clinical laboratory physicians and scientists at UC San Diego (La Jolla, CA, USA), builds upon two assays developed by Diazyme Laboratories, Inc. (Poway, CA, USA).

The presence of novel coronavirus antibodies can reveal persons who may have unknowingly contracted COVID-19 and recovered, but never showed signs of infection. The tests analyze blood samples, similar to those taken for routine clinical reasons, for the presence of two of the body’s five classes of antibodies: IgG and IgM. Antibodies are proteins used by the immune system to recognize and help neutralize pathogenic invaders, such as viruses or bacteria. The IgG antibody is the most abundant type; IgM is one of the first antibody types produced by the body’s immune system to fight a new infection. Looking for these two types of antibodies together, rather than one, increases the treating physician’s confidence in being able to differentiate between a recent infection versus a past exposure to the SARS-CoV-2 virus.

The twin Diazyme tests have shown high sensitivity and specificity, particularly compared to most point-of-care, rapid-response serological tests for novel coronavirus now flooding the international market. So far, only one rapid serological test, which claims a result within 15 to 20 minutes, has received Emergency Use Authorization from the US Food and Drug Administration (FDA).

The coronavirus blood testing program at UC San Diego Health is, for now, open-ended and will be overseen by the UC San Diego Center for Advanced Laboratory Medicine (CALM), which houses the majority of UC San Diego Health’s Clinical Laboratories and related research activities and is already the hub for the health system’s in-house PCR-based diagnostic testing of patients and persons suspected of having COVID-19. The initial capacity for serological testing will be a combination of up to 1,200 of IgM or IgG antibody tests per day, with results within 24 hours and the system being scalable.

The first testing cohort will likely be health care workers, which will help identify who are now in a convalescent phase after a documented exposure and, perhaps, may have acquired at least some degree of immunological protection. At this point, it has not been established whether the presence of IgG antibodies is an indicator of immunity to SARS-CoV-2 infection or re-infection, as seen with many other viral infectious diseases. Aside from identifying past coronavirus exposure, serological testing will likely be a valuable epidemiological tool. There are expansive plans to use blood tests to map where the virus has spread, which cities, states and regions may have developed some degree of “herd immunity” to future outbreaks and which places and populations remain at greatest risk.

“These tests have already gone through an initial assessment and validation by Diazyme,” said Robert Fitzgerald, PhD, professor of clinical pathology at UC San Diego School of Medicine and director of the Toxicology Laboratory and associate director of Clinical Chemistry Laboratory at UC San Diego Health. “We’ve put them through our validation processes as well, including comparing samples from patients known to have COVID-19, healthy volunteers and blood samples from 2018, long before the virus appeared.”

“This is part of the next wave of testing,” said Ronald W. McLawhon, MD, PhD, director of CALM and UC San Diego Clinical Laboratories and chief of the Division of Laboratory and Genomic Medicine. “It’s intended to answer those growing questions about who has been infected and who might still be vulnerable to exposure.”