There are two methods of testing available to detect COVID-19. Molecular assays and immunoassays. Currently, India is using molecular assays. These can be manual or automated. An oral swab is taken from a suspected person and Viral Ribonucleic Acid (RNA) is isolated from these swabs using a variety of chemicals. But this amount is very small, it is impossible to figure out the pathogen directly from this sample. To increase the test material, the polymerase chain reaction technique (PCR) is used. The coronavirus is an RNA virus and to use the PCR technique in such a sample, an additional step of treating the sample with enzyme reverse transcriptase is needed. Once the RNA is converted to a complementary strand of Deoxyribonucleic Acid (DNA), this DNA can be replicated many times over — generally 40 time. During the replication process, other than primers (which are specific to the viral genetic material), enzymes and nucleotides, fluorescent probes are added. These fluorescent probes are released from each strand when the copying of the strand is complete and provide a visual signal. If the sample had the coronavirus RNA, replication would occur and the visual signal would be there. So far, India has been using imported RT-PCR test kits. On March 23, 2020, the Indian Council of Medical Research (ICMR) approved two test kits after finding them to be 100 per cent sensitive to true positive and true negative samples
Other than the PCR technique, rapid tests have been launched in the market. These are immunoassays, which can be both manual or automated . These follow the same principle used in pregnancy tests. They identify the IgM and IgG antibodies developed against the SARS-CoV-2. For the test, whole blood, serum and plasma can be used and if antibodies are present in the sample, these bind to the antigen immobilised on the test strip and give a coloured reaction. Such test kits are easy to use, provides quick results and also are effective in identifying asymptomatic patients. But there is a risk of getting false positives and results need to be confirmed using a more advanced test. Many such tests are available globally but not in India.
