India’s rapid antigen tests risk belittling virus spread, says diagnostician

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India's high use of antigen tests risked underestimating the actual spread of coronavirus, warned the head of a top diagnostic firm on Wednesday. Representational image.

India’s rapid antigen tests risked underestimating the actual spread of coronavirus, warned the head of a top diagnostic firm on Wednesday. According to him, the fast but less accurate “rapid antigen tests” now account for India’s 60% of all coronavirus tests.

The firm estimated that India’s high use of antigen tests could misrepresent the actual spread of the infection.

Antigen devices return results in about 15 minutes compared with several hours for the reverse transcription polymerase chain reaction (RT-PCR) method, a laboratory-based process which the US Centers for Disease Control and Prevention calls the “gold standard here” for COVID-19 detection.

Whereas antigen tests typically detect the virus around 80% to 90% of the time, lab-based tests detect the virus more than 95% of the time, say regulators and health experts in countries like the United States.

India’s high use of antigen tests a wrong scale

As a consequence of the reduced accuracy, India’s high use of antigen tests compared with a global use of around 10%, risked underestimating the spread of coronavirus, according to the founder of Mumbai-based Thyrocare Technologies Ltd, one of India’s top-three diagnostic chains.

“It’s a wrong scale used to assess” the extent of the spread of the virus, Arokiaswamy Velumani told Reuters.

The total number of coronavirus cases reached close to 8 million on Wednesday. But India’s official tally shows daily new cases have dropped sharply since a mid-September peak.

Velumani said Thyrocare’s centres are now receiving only about 2,500 samples a day for RT-PCR tests. However it was a high of about 7,000 samples in September.

The health ministry and the ICMR did not immediately respond to emails from Reuters seeking comment on Velumani’s comments.

RT-PCR dominates in the US but authorities there are planning to increase the use of antigen tests to screen people.

The Union health ministry has not provided a breakdown of the test methods deployed. But State and Central officials repeatedly defended the use of antigen tests to quickly identify infections of 1.3 billion people.

It has also helped India quickly ramp up its testing capacity to 1.5 million samples a day.

“There was a stigma that India was not doing enough tests,” Velumani said.

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