NEW DELHI, Sep 11: Rapid antigen tests (RAT) for Covid-19 are cheaper and deliver quicker results but should be no more than an adjunct to the more reliable RT-PCR tests because of the potential for false negative results, say scientists.
The union health ministry’s move on Thursday to direct all states and union territories to mandatorily retest all symptomatic negative cases of RATs with RT-PCR is the right strategy, they said.
The ministry noted that symptomatic cases tested negative by RATs are not followed up by RT-PCR testing in some large states. The idea is that no positive Covid-19 cases are missed.
Labelling RATs “spuriously comforting,” immunologist Satyajit Rath said it is also known that there are false negative outcomes in the tests.
The Indian Council of Medical Research (ICMR) knew this all along and advised RAT-negative symptomatic people to be retested with RT-PCR tests, the scientist from New Delhi’s National Institute of Immunology (NII) told PTI.
Virologist Shahid Jameel added that RATs have a field sensitivity of 50-60 percent and show many false negatives.
“If someone has symptoms, he/she should be retested. This is the correct thing to do,” Jameel told PTI.
RT-PCR tests ‘amplify’ viral RNA while detecting it, but antigen tests do not do any such amplification of the detected viral protein, the experts noted.
Because of this amplification step, RT-PCR tests for viral RNA are more sensitive than antigen tests, they said. (PTI)