Antigen tests for Covid-19 will start in the state, chief minister Mamata Banerjee said on Wednesday. People near the Chetla market who have Covid symptoms will be made to undergo the antigen test, a Calcutta Municipal Corporation official said.

Metro spoke to microbiologists and doctors to understand what the test is and how it will help.

What are antigen tests?

The nasopharyngeal swab is examined to detect the presence of the virus. Antigens are foreign bodies that enter the human body and trigger an infection. These tests will detect the antigens. They are called rapid antigen tests as well.

How are they different from the current swab tests?

The swab tests (RT-PCR tests) take at least a day to give the results. The antigen test results will be available in 30 minutes. The RT-PCR test, though, is the best to detect Covid-19, doctors said.

Has the ICMR approved antigen tests?

Yes. An ICMR advisory issued on June 14 (available on its website) said it approved the tests and that it had been evaluated by the ICMR and the All India Institute of Medical Sciences.

Are these confirmatory tests?

A positive result will indicate the person is infected with the novel coronavirus, a microbiologist with the ICMR said. But one cannot rule out infection in people testing negative, the microbiologist said.

A person who tests negative but has symptoms should be tested using the RT-PCR method, according to state guidelines.Someone who is asymptomatic can be declared negative.

Then why are the tests being done?

Because they give results fast. Those who test positive can be isolated quickly and the spread of infection prevented better. These tests will help Covid-19 suspects seeking admission to hospitals.

Those who are asymptomatic but need hospitalisation for chemotherapy or organ transplant, or HIV patients, immunosuppressed patients and those aged above 65 with comorbidities can go for the rapid antigen tests.

The state government has supplied antigen test kits to many government hospitals to test people in the high-risk category.

Does it mean anyone can get an antigen test done?

No. The ICMR has not approved individual laboratories to conduct antigen tests.

The CMC action plan

The CMC plans to conduct antigen tests in places, which have reported many cases, a CMC official said. People with symptoms and those detected in the surveillance conducted by civic health workers will be encouraged to go for the test. The CMC will conduct RT-PCR tests on those who have symptoms but have tested negative in antigen test.