Rapid antigen tests (RAT) now made up 25%-30% of the tests that were being conducted in India, Dr. Balram Bhargava, Director-General, Indian Council for Medical Research (ICMR), said at a press briefing on Tuesday.
According to the latest testing figures, the ICMR said it had tested nearly 6.6 lakh samples in a single day and, overall, India had tested over 20 million samples. The agency, however, has not provided a break-up of how many of these tests were RAT, and Dr. Bhargava’s statement is the first indication by the agency of the growing importance of this test.
RAT tests are quick tests and are said to be very reliable in confirming if someone is positive for the virus. However, it has a low sensitivity, meaning that it can also miss — sometimes as many as 50% — of those who may be carrying the infection. Therefore, the ICMR advisory has been to retest all those who test negative for the test and those who manifest symptoms.
While some States individually provide data on how many of their daily tests constituted Rapid Real Time Polymerase Chain Reaction ( RT-PCR) and how many RAT, not all reveal how many individually tested positive on both these tests. Only the Delhi government told the Delhi High Court last month that 0.5% of those that tested antigen-negative were retested.
Critics have pointed out that not retesting enough negatives, as per ICMR guidelines, will lead to several asymptomatic infections being undetected, and whet the spread of the infection.
“When we started antigen tests, they were about 5%-6% of the total tests and they are constantly rising to about 25%-30%,” he said in response to questions, “It takes about five days for fever-like symptoms to manifest and there's a big chance that in that period, both RT-PCR and antigen tests may miss detecting the virus. The same goes for asymptomatics. In that way, both are similar for finding a positive case. States have been told to use an intelligent and calibrated testing policy depending on which area needs more testing and setting up labs there.”
Maharashtra, Delhi, Telangana are major users of antigen tests.
The antigen tests are made by SD-Biosensor, a South Korean company that is manufacturing its kits in Gurgaon, Haryana. It uses a nasal swab and can detect within 30 minutes if a sample contains the virus. Unlike an RT PCR test which is far more accurate, it does not need samples to be transported to a laboratory for analysis.
