The ICMR has suggested that a person may test positive or negative on the basis of when and which test is conducted.
COVID-19: As the number of cases of coronavirus is rising throughout the country, the ICMR that has been leading India’s response to the coronavirus has brought in some much-needed reform in its guidelines for Covid-19 testing. It has approved Covid-19 ELISA test kits other than those that are based on its own technology.
As per an IE report, here are the different modalities of Covid-19 testing in India:
An ELISA test is based on the detection of immunoglobulin G (IgG) and immunoglobulin M (IgM). Also, in India, this test is approved only for sero surveys, which estimates the exact proportion of a population that has been exposed to the coronavirus infection. The presence of IgG infers antibodies formed in the later stage of infection while the presence of IgM shows early stages of infection. The ICMR had in May designed a Covid Kavach ELISA IgG test through the National Virology Institute, Pune. As many as seven pharmaceutical companies— Zydus Cadila, Meril Diagnostics, Voxtur Bio, Trivitron Healthcare, J Mitra & Co, Karwa Enterprise, and Avecon Healthcare are currently producing ELISA kits based on ICMR-developed technology. Now, ICMR has certified ELISA kits developed by Mumbai-based Transasia Bio Medicals and Euroimmun US Inc.
RT-PCR is the globally accepted test for the coronavirus infection. This has been the go-to procedure for the ICMR for covid -19 testing till now though it is known to be expensive, However, this test is free in government labs. Earlier it was also used for diagnosis of Ebola and Zika. In the RT-PCR test, pathologists collect swabs from the nasal and oral tract of the suspects to look out for the viral RNA to confirm the presence of SARS-CoV-2 that causes Covid-19. The test is free in all government-run labs while ICMR had earlier capped the cost of tests at private labs at 4,500. ICRM has now taken away that capping and has allowed state governments to fix their own cost. Until now, the ICMR has evaluated 97 kits of various manufacturers for RT-PCR testing, of which 40 have so far been approved.
Rapid antibody test
This test method is the cheapest of all methods that can be used to detect SARS-CoV 2 in the human body but it is used for population surveys only. It takes hardly 20 minutes to detect the presence of antibodies in a human body, however its inaccuracies can’t be ruled out. Rapid antibody tests can’t differentiate between antibodies produced in the body in response to coronavirus infection and other infections and hence it can’t be ruled as a confirmatory test for the Covid-19 disease. People testing positive in the rapid antibody test will have to undergo an RT-PCR test to confirm Covid-19. Notably, the ELISA is considered to be more accurate than this rapid antibody test.
This method of testing can be used to detect pools of people who have been infected in any hotspot areas. So far, the ICMR has considered 46 rapid testing kits for evaluation and has given its approval to only 14 of them including eleven Indian manufacturers. As per the ICMR, a person can test positive for antibodies 7-10 days after contracting Covid-19 infection and can continue to display positive results for several weeks.
The rapid antibody test is based on the collection of blood samples from suspects’ finger, their plasma, or serum. The test costs Rs 600.
This is a private test, which works on the same principle as RT-PCR, but with a smaller kit and faster outcomes. The ICMR has recently approved TrueNat for Covid-19 for screening and confirmation. As per the ICMR guidelines, If a sample test is negative, it must be treated as negative while if a sample tests positive, then a second test should be done to confirm the RdRp gene. The TrueNat computer is compact and lightweight and it runs entirely on batteries and delivers results within 60 minutes. This includes taking swabs at the nasal or oral levels.
COVID-19 testing time and when to use what test
The ICMR has suggested that a person may test positive or negative on the basis of when and which test is conducted. A suspect may test positive by RT-PCR or TrueNat in the early days of infection as these tests involve the collection of samples from respiratory tracts while at the same time the same suspect may test negative by ELISA and Rapid Antibody test. As soon as the immune cells of an infected body start producing antibodies against the virus, the suspect will test negative by RT-PCR and TrueNat while test positive by Rapid Antibody Test. Therefore, the difference in the timing of the test may produce different results on the same suspect.
Most importantly, keep in mind that for the purpose of diagnosing and treatment, doctors across the world rely on RT-PCR as it detects infection in an early and active stage.