Ascertain accuracy of rapid antigen tests: Government to ICMR

NEW DELHI: The government has asked ICMR to evaluate the accuracy of rapid antigen testing (RAT) in detecting coronavirus through mathematical modelling and analyse if the proportion of false negatives is substantially high, as has been suspected in some instances, official sources said.


“We have asked ICMR to check the accuracy level mathematically by assessing how many samples are symptomatic but report negative in rapid antigen tests and then what is the average percentage which turn out positive on a repeat test with RT-PCR. This has to be assessed on samples from across the country. If there are concerns, they need redressal. Once it is done , we can be assured that our numbers are correct,” a senior official told TOI.

While use of antigen tests helped ramp up testing significantly across the country, false negatives and missing repeat tests to confirm through RT-PCR has led to concerns that this might lead to wider spread. The tests need to be conducted carefully and also the RT-PCR testing of persons with symptoms who test negatively has to be done scrupulously.

“It is well recognised that antigen tests have a lower sensitivity than RT-PCR tests which themselves have a modest sensitivity of around 60%. So, antigen tests by themselves are likely to miss more than half of the Covid-19 infected cases. Wherever there is strong suspicion on grounds of clinical features or contact history, RT-PCR must be performed for antigen negative cases. If clinical features are strongly indicative, even a negative RT-PCR test should not dissuade from treating the person as a Covid-19 case,” says Public Health Foundation of India (PHFI) president K Srinath Reddy.

According to ICMR’s protocol, any sample testing negative through RAT will have to be mandatorily retested with RT-PCR if the person demonstrates symptoms. Those testing negative with no symptoms are to be monitored for a few days. If they develop symptoms then they are to undergo RT-PCR testing too.

In Delhi, 15% of symptomatic individuals who tested negative in RAT were found to be positive in a second confirmatory RT-PCR test. The total number of such persons tested was however less than 3,000. The total tested by the RAT method was close to 3 lakh.

India has been testing more than 5 lakh samples in a single day to check Covid-19 over two consecutive days. Cumulatively, India has so far tested more than 1.73 crore samples. The tests per million stands at 12,562.