Can antibody tests accurately detect prior SARS-CoV-2 infection?

What is it about?

When the COVID-19 pandemic first struck, the disease spread rapidly. To control this, it became imperative to identify and isolate people infected with SARS-CoV-2. However, a large proportion of these people did not show any symptoms of infection. How, then, could these people be identified? One possible answer was: through antibody testing. Humans that have been previously infected with SARS-CoV-2 would have antibodies against the virus. These antibodies are present in serum (the liquid part of the blood). They can be identified using chemiluminescence immunoassay (CLIA) techniques even after someone has recovered from COVID-19. While CLIAs can process a large number of samples at a time, they have not been assessed in patients with COVID-19 beyond 35 days of symptom onset. A 2021 study aimed to address this gap. In the study, scientists compared the accuracy of three popular CLIA techniques: a chemiluminescent microparticle immunoassay (CMIA), a luminescence immunoassay (LIA), and an electrochemiluminescence immunoassay (ECLIA). To do this, they tested samples from three groups: 1. 145 people with confirmed SARS-CoV-2 infection, 2. 191 healthy blood donors, and 3. 1002 healthcare personnel. People in the latter two groups did not have prior evidence of COVID-19. All three techniques were found to be accurate in diagnosing SARS-CoV-2 infection, even in the presence of other viral infections.

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Photo by ANIRUDH on Unsplash

Photo by ANIRUDH on Unsplash

Why is it important?

Serologic testing can: 1. Tell us the prevalence of COVID-19 in a population, 2. Assist contact tracing and surveillance efforts, and 3. Identify and profile those with a higher risk of getting infected. From a public health perspective, this information is very important. It helps governments determine the next steps required to control disease spread, and how effective these steps would be. KEY TAKEAWAY: CMIA, LIA, and ECLIA seem promising for the retrospective detection of COVID-19, even 47 days after symptom onset. Their reliability can be further improved by: 1. Assigning assay cut-off values, 2. Introducing “grey zones” (results which are half of the recommended cut-off to assign a positive value), and 3. Using another confirmatory test to augment the first. However, the reliability of these tests may vary in areas with low disease incidence.