Karnataka sees a drop in RT-PCR tests as government pushes for cheaper antigen kits

Bengaluru: As Karnataka ramps up Covid-19 testing through the cheaper rapid antigen test kits, the number of RT-PCR tests, considered more accurate in detecting the infection, has dropped.

Before the government started using rapid antigen kits, between 20,000 and 24,000 Reverse Transcription-Polymerase Chain Reaction tests were done every day.

However, the numbers have come down to 9,000-12,000, especially over the last two days, after the state government began to aggressively push rapid antigen tests.

These tests, known to deliver quick results, are less accurate with a sensitivity rate of 50.5% to 84%.

The more expensive RT-PCR test is considered the gold standard in detecting Covid-19 infections.

Of the 42,458 tests done on August 3, 29,488 (69%) were rapid antigen tests, while 12,970 (30%) tests were performed using RT-PCR kits.

A day prior to that, of 27,989 tests, 18,074 (64%) were on antigen and 9,915 (35%) were RT-PCR tests.

“Rapid antigen test became the focus and target driven, reducing the number of RT-PCR tests. However, RT-PCR is being increased now,” a government official said, adding that though total tests are up, rapid antigen tests show considerable false negatives. A positive report in an antigen test is considered definitive, but a negative report will be further referred for an RT-PCR test if the person is symptomatic.

About 24% of the samples referred for retesting on RT-PCR have turned out positive in the state.

Officials said the government had not issued any advisory to reduce RT-PCR tests but has only asked for the rational use of test kits.

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District officials told ET that there were certain gaps in referring symptomatic people with negative rapid antigen reports to retest using RT-PCR. “Either the staff who collect samples do not maintain a clear record of people who are symptomatic and asymptomatic, or people do not show up for retesting,” a district official said.

Dr CN Manjunath, in-charge of lab testing in Karnataka, said the state will make it mandatory to collect samples for both rapid antigen and RT-PCR testing at one go. “So, if the person is symptomatic and the test comes negative on antigen, samples can be immediately sent for the RT-PCR test,” he said. On the decrease seen in RT-PCR tests, he said “it is the right strategy.”

Dr R Giridhar Babu, ICMR task force member on surveillance and research of Covid-19, said the focus should be on increasing the tests. “Bengaluru is testing 9,000-10,000 samples a day, of which 2,000 people test positive. The positivity rate in the city is high. We should test 10 times more to ensure we are not missing out on cases,” he said.



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