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Amitabh Bachchan and son Abhishek Bachchan tested positive for coronavirus via Rapid Antigen Test (RAT) in Mumbai. What is RAT and how reliable it is?

Bollywood actors Amitabh Bachchan and Abhishek Bachchan initially tested positive for coronavirus on Saturday. The same antigen test was also conducted on Aishwarya Rai Bachchan and daughter Aaradhya Bachchan which came negative initially but the same test when conducted two days later showed the two as positive for COVID-19 as per a tweet from Abhishek Bachchan. However, his mother Jaya Bachchan tested negative for the virus.

What is Rapid Antigen Test (RAT)?

Indian Council of Medical Research (ICMR), on June 18 has approved another kind of diagnostic test for COVID-19 which is to be deployed under specific settings, called antigen test. This test is currently in use in Delhi and Mumbai.

These tests can be used under three settings:

1. Containment Zones: Antigen tests give immediate results so ICMR has approved the deployment of this test in containment zone where all those who show symptomatic influenza like symptoms and asymptomatic contact cases are tested. The test kit needs to be stored between 2 to 30 degrees Celsius.

2. Health Care Settings: Hospitals with patients having flu symptoms, high risk patients and patients seeking hospitalisation under emergency can be tested through RAT.

3. Asymptomatic patients: The last setting is the group of people who come under asymptomatic patients undergoing aerosol generating procedures.

How does Antigen test differ from RC-PTR?

Rapid Antigen Test gives the result in less than 30 minutes unlike RC-PTR test which takes 6 to 24 hours for the results.

While the RC-PTR test looks for viral RNA in the body, antigen test looks for viral protein in the body. Samples for both the tests are collected via throat or nasal swab.

Antigen Tests, being quick can be used in areas that require more number of tests. The antigen test is already in wide use in Mumbai and Delhi. Only one company has got the approval to make antigen test kits which is a South Korean company, S D Biosensor.

How efficient is Rapid Antigen test?

While comparing the tests and to know the efficiency of antigen test, we must know the sensitivity and specificity of the antigen test.

Sensitivity refers to the detection of truly positive coronavirus patient while specificity refers to the ability of this test to identify the negative patients.

The specificity of this rapid antigen test is about 99%, so if someone’s is positive according to this test, it can be truly relied upon. Sensitivity of the antigen test is reported to be 50% to 80%. So, it can miss several positive cases. The same happened in case of Aishwarya Rai and her daughter during initial testing.

In a nut shell, a positive antigen test result is a confirmed case of coronavirus and a negative antigen result should be followed by an RC-PTR test.

By Gayatri Yellayi