New Delhi: On Monday, a day after the Centre announced that an IgG ELISA test for detection of antibodies to Covid-19 had been developed, it released a document outlining details of surveillance to be carried out in all districts to check for the prevalence of infection using the same.
Pune-based National Institute of Virology has developed an immunological assay — enzyme-linked immunosorbent assay (ELISA) — that can detect antibodies that are developed in response to the coronavirus infection. Health Minister Dr Harshvardhan said this the first test of the kind to be developed in India and it will play a critical role in surveillance of proportion of the population exposed to the virus. But what is an ELISA-based antibody test and how is it different from the RT-PCR tests? Here, News18.com explains.
Q.What is an ELISA-based test?
The Enzyme-Linked Immunosorbent Assays (ELISAs) based test is a laboratory technique used for the detection of antibodies that are produced by the body to fight against antigens or foreign substances. ELISA-based tests are blood-based tests, which have high sensitivity and specificity. The sensitivity of a test refers to the percentage of results that will correctly find out the presence of infection in a person and specificity refers to the percentage of results that will correctly find out whether or not a person is infected.
According to the union health ministry, the ELISA-based antibody test developed by the National Institute of Virology, Pune, has a sensitivity of 92% and its specificity is 97%. The test involves drawing the blood of the person. The sample is then placed inside the small wells of an ELISA plate. These plates are coated with the antigen or the inactivated form of the virus. If the blood contains antibodies, it binds to the antigen and a substrate solution is added to the well. The reaction usually produces a colour change, thus detecting antibodies. ELISA tests can be done manually or in a semi-automatic and automatic way.
Q.What do we know about the kit developed by NIV-Pune?
The ELISA-based test developed at National Institute of Virology, Pune, is called COVID KAVACH ELISA. The test kit has been validated at two sites and as mentioned above, has high sensitivity and specificity, thus making it a better tool for surveillance of infection spread in a community compared to the rapid antibody test kits. The test also has the advantage of being able to evaluate 90 samples together within 2.5 hours, allowing labs to run many samples in a day.
It is an IgG Elisa-based test. This means that the test will be done to detect the Immunoglobulin G (IgG) antibody. The body produces Immunoglobulin M (IgM) and IgG antibodies to fight against a pathogen. The IgM antibodies are produced in four-seven days after pathogens enter the body while 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 will the government use the kits developed by NIV-Pune?
In an outline made public on Monday, the central government has said that the ELISA-based test kits will be used as part of surveillance to monitor the prevalence and trends of SARS-CoV-2 infection at the district level. The central government has said that health facility-based surveillance and sero-survey will be done to check the presence of the infection. This surveillance exercise will also give insights into possible community transmission across the country. The health ministry has asked state governments and district administrations to collect 800 samples from a district per month as part of the surveillance.
Q.How is it different from rapid antibody kits and RT-PCR tests?
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.
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