COVID-19 Testing Explained: How Is It Done & What Is Rapid Antibody Testing?

To test for COVID-19 the Reverse Transcription Polymerase or RT-PCR and the Rapid Antibody Test are utilized. Find out what they are and how it is used.

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New Delhi: COVID-19 positive cases have reached over 20,000 in India. The data is not absolute as there is a lack of testing kits available in the market and in the country, which is why testing is mostly done through contact tracing. Contact tracing according to WHO is closely watching the contacts of an infected person to track whether they have contracted the disease so that they can get care and treatment if necessary, which will prevent further transmission of the virus. The reason why India has opted for surveillance over mass testing is because of the shortage of testing kits available. There two main ways to test whether a person has COVID-19- Reverse Transcription Polymerase or RT-PCR and the Rapid Antibody Test to detect the presence of the virus. How does testing work? There two main ways to test whether a person has COVID-19. The first being reverse transcription-polymerase chain reaction or RT-PCR, this test takes nasopharyngeal swab or sputum sample. This test can detect as little as one virus particle present in person, but this test can only tell if the person is currently infected or not. It cannot tell whether a person was infected earlier and has recovered. The test results can take anywhere between a few hours to 2 days. The test carried out by swab isn’t reliable because the virus can disappear from the throat and multiply from the lungs. This is why a sputum test is much more effective, especially for a person testing on the second week from exposure. Also Watch: Will herd immunity help stop Coronavirus? The second method is through Serology, which takes the blood sample. Immunoglobulin detection tests are based on the qualitative detection of IgM and IgG that are specifically generated by the body in response to SARS-CoV-2 infection. IgG antibodies to SARS-CoV-2 generally become detectable 10–14 days after infection although they may be detected earlier, and normally peak around 28 days after the onset of infection. Assays can be performed in central laboratories (CLT) or by point-of-care testing (PoCT) aka Rapid Antibody Test. The results can take up to a few minutes to a couple of hours. How does Rapid Antibody Test work? Rapid Antibody Test works in a similar manner as a pregnancy test but with a blood sample. Collect 2-3 drops of fresh blood/serum or plasma and place it in a sample container and place 2-3 drops of the buffer provided in the same container (cassette). The cassette allows the diluted sample to move by capillary action. The cassette has SARS-CoV-2 antigen that may bind chemically with either IgM or IgG; thus, forming an antigen/antibody complexes of antigen/IgG and/or antigen/IgM and helping to detect the presence of the virus as it tells us if the body is fighting an infection. The test kit has a control line, a G line which shows the presence of IgG (Immunoglobulin), an M line which shows IgM (Immunoglobulin), and a negative line which will indicate if the body has no antibody. Generally during an infection, the body’s first line of defense is with IgM immunoglobins while the IgG is produced later. According to an article in the medical journal The Lancet ‘Antibody tests are different because they require some knowledge of the proteins that form the viral coat—specifically, those proteins to which the immune system responds, triggering the production of antibodies that flag or neutralize the virus.’ Although the Rapid Antibody is not as accurate as RT-PCR, they are faster. The PCR tests work on DNA but since the coronavirus is an RNA virus it is first converted to DNA which takes time. That is why Rapid Antibody testing is highly effective in contact tracing or testing in large volumes for example in hotspots. The ICMR considers this test as a supplementary test that can indicate the presence of a disease in a specific area. According to some reports, India is still import testing kits and since there is a global demand for these kits India like many countries is running short of these kits. The ICMR has only approved only one homegrown kit, although tests are being carried out to make testing far more efficient and quicker.