The Indian Council of Medical Research (ICMR) has advised the States to conduct serological-surveys to measure the coronavirus exposure in the population using IgG ELISA Test.
As per the direction of the council, the coronavirus (COVID-19) exposure in the general population as well as in high-risk populations would be measured and the outcome will help “decide the future course of action against the pandemic”.
Q. What is an ELISA-based test?
A. The Enzyme-Linked Immunosorbent Assays (ELISAs) based test is used for the detection of antibodies that are produced by the body to fight against antigens or foreign substances.
Q. How is it carried out?
A. ELISA-based tests are blood-based tests, which have high sensitivity and specificity.
1. The test involves drawing the blood of the person.
2. The sample is then placed inside the small wells of an ELISA plate.
3. These plates are coated with the antigen or the inactivated form of the virus.
4. If the blood contains antibodies, it binds to the antigen and a substrate solution is added to the well.
5. The reaction usually produces a colour change, thus detecting antibodies.
Q. What is IgG?
A.Immunoglobulin G (IgG) is an antibody.
The body produces Immunoglobulin M (IgM) and IgG antibodies to fight against a pathogen.
1. The IgM antibodies are produced in four-seven days after pathogens enter the body.
2. The IgG antibodies are produced between 10-14 days of the pathogen's appearance. If the IgG antibody is detected, it can be concluded that the person was exposed to SARS-CoV-2.
Q. How is it different from rapid antibody kits and RT-PCR tests?
A.ELISA is also a form of a rapid test. However, other rapid antibody test kits are point-of-care and use a finger- prick method to draw blood. They take much lesser time and do not need a laboratory process to detect antibodies.
Both, ELISA-based tests and point-of-care tests are not used for confirming Covid-19 infection and are only used for surveillance purpose.
Those who test positive using these tests are usually tested with RT-PCR tests.
RT-PCR tests are considered as the gold standard for confirming the presence of SARS-CoV-2.
RT-PCR is a time consuming, lab-based test and involves the collection of throat and nasal swabs and is not a blood-based test.