BENGALURU: The State government is ready to try the rapid antigen-based testing method for COVID-19, which was approved by ICMR recently. It gives faster results compared to the RT-PCR method, and also detects the virus, unlike the rapid antibody test which detects antibodies.
Nodal officer for COVID-19 testing in the state, Dr CN Manjunath, who is also director of Jayadeva Institute of Cardiovascular Sciences and Research said, "Two to three weeks after the kits are made available by the company — SD Biosensor — we might place an order. It is also diagnostic, like RT-PCR. It can provide results in 5-10 minutes, unlike RT-PCR, which takes six to eight hours. TrueNat and CBNAAT tests take two hours, but can only test a small number of samples at a time."
It is cost-effective, at Rs 450 per sample, as opposed to RT-PCR, which costs around Rs 2,000. It does not require a sophisticated lab set-up or pose a bio-safety hazard. Dr Manjunath added that it can be used at the field level to diagnose the virus.
Dr Sujay Prasad, technical director of Neuberg Diagnostics, which tests Covid samples, said antigen testing involves taking a nasal swab from the person, and the test detects the spike protein. "If the result is positive, it is a true positive, but if it is negative, a sample will have to be sent for RT-PCR testing, for confirmation. This is because the specificity (ability to detect the virus correctly) of antigen test is 99.6 per cent, but the sensitivity (ability to pick up negatives clearly) is only 50 per cent. If there are 100 cases, the test can identify only 50 of them as positive for coronavirus," Dr Prasad explained.
While the time taken to get results is faster than that of RTPCR, there are some practical difficulties. "The ICMR has said that viral transport medium used in RT-PCR cannot be used for antigen. The manufacturing company has said that a different buffer, which is like a viral transport medium, will have to be used for this test. The swab has to be taken twice, one for antigen testing and another to be sent for RT-PCR confirmatory test, in case the result is negative," Dr Prasad said.
One practical difficulty is that the antigen test has to be done within one hour of collection, he added. The big benefit is that it can be done at the field level — by a hospital or nursing home — and all samples need not be sent to a central lab.
Additional Chief Secretary, Health and Family Welfare department, Jawaid Akhtar said, "We are planning to use both antibody and antigen test. The antigen test will help us find the virus load, but it has to be supported by RT-PCR test. The government of India got approval for antigen test just a fortnight ago, and we are also planning to do it. However, the kits have to be procured."