Know About A COVID-19 Antibody Test, Also Known As A Serology Test

Did you know Serology testing does not help detect the presence of the virus, but rather allows detecting the antibodies that are, or were produced by the body in fighting the disease?

By Dr. Prerna Agarwal, Technical operations, Apollo Diagnostics 

It has been more than 7 months and India is still fighting the Coronavirus pandemic.  The antibody or serology test is a blood test that helps look for signs of the previous COVID-19 infection. It helps detect antibodies that are proteins in the blood and help fight off infection.

Antibody testing is promising as it will help us understand one of the pervasiveness of COVID-19 in people. The fact also remains that only antibody testing should not be relied on while detecting Coronavirus. This will suggest that even if you receive a positive antibody result, showing that COVID-19 antibodies were detected, there is no certainty that one will get COVID-19 again.

Antibody test or serology test tells if one is infected in the past

  • When people get infected with viruses such as SAR-CoV-2, their body mounts an immune response by developing antibodies against the particular virus. These antibodies may attack the virus and help eliminate the virus from one’s system.
  • If someone contracts COVID-19 but shows no symptoms then Antibody tests also known as serology test, tell us if an individual was infected in the past and whether an immune response has.
  • Are you aware that there are two types of tests for SARS-CoV-2 which provide different kinds of information? There is a diagnostic test that will allow one to tell if someone is  recently infected.
  • Whereas talking about the serology test, it does not detect the presence of the virus, but rather detects the antibodies that are, or were, produced by the body in fighting the disease. Did you know that the antibodies are proteins produced by one’s immune system in response to an infection and are specific to that particular infection? They are present in the liquid part of the blood called serum or plasma.
  • Immunoglobulin M, or IgM, is the first type of antibody produced in response to an infection and is detectable 4 to 7 days after the infection starts. IgM antibodies are short-lived and their existence signals a new infection is present.
  • Immunoglobulin G, or IgG, antibodies are produced 7 to 14 days after infection. These antibodies can be detectable for weeks, months or over years, based upon the antigen and the individual. Since we don’t know a lot about SARS-CoV-2, as it’s a new virus, we don’t know how immunity against this virus works.

Total assays: These are combined IgG-IgM tests, which cannot distinguish between early IgM and late IgG antibody responses. As a result, total assays can’t reveal whether a person has the IgG antibodies that are needed for long term immunity, or if they are currently infected. IgG and IgM antibodies to SARS-CoV-2 are can be detected in the blood several days after one suffers from an initial infection. Although, the time for which antibodies are present post-infection is not well characterized.

Keep in mind: Various studies have shown that severe and those cases that were critical had higher IgM levels than compared to the mild cases, whereas the IgG level in critical cases was lower than in mild and even the ones with the severe cases. It can happen because of the high disease activity and/or a compromised immune response in critical cases that one has.

The IgM antibody levels were slightly higher in deceased patients than the ones who recovered. But, IgG levels in these groups did not significantly differ. IgM levels rapidly went down in recovered patients, whereas in deceased cases, either IgM levels remained high or both IgM and IgG were undetectable during the disease were present. Thus, the right type of serology test could help us understand immunity against COVID19 at an individual and a population level.

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