Private diagnostic laboratories, hospitals and online aggregators are marketing COVID-19 antibody tests as quick, cheap diagnostic tests and even as immunity certificates. But antibody tests, which are very useful tools for disease surveillance, have limited use in clinical diagnosis—a distinction that a non-specialist customer is unlikely to know. In the absence of clear directions from either the Indian Council of Medical Research or from the Ministry of Health and Family Welfare, these private healthcare players seem to be using antibody tests to cash in on public anxiety in a pandemic.
Antibody tests, also called serological tests because they measure antibodies in serum, are useful for understanding whether there has been an outbreak of disease. For instance, antibody tests are being used in serological surveys in cities like Delhi, Mumbai and Pune to gauge the spread of COVID-19. But they cannot tell us whether a person is infected at the time the test is conducted. This is because antibodies develop weeks after the onset of infection and sometimes after a person has recovered from symptoms. They have little value for people trying to decide whether they need treatment.
Yet, private laboratories are administering the tests to individuals seeking diagnosis. In early August, Aman Arya, a merchant navy officer from Bhagalpur in Bihar, took the antibody test from Thyrocare, a diagnostic laboratory chain with its headquarters in Mumbai, to check whether he was infected with COVID-19. He needed a certificate showing that he was not infected in order to join a new posting at Kandla in Gujarat. Thyrocare and other companies are offering two kinds of COVID-19 antibody tests. The first is a complete antibody test for all types of antibodies that might be produced in response to an infection and the second tests only for the IgG antibody, which develops later in the immune response but lasts longer. Testing positive on either only indicates that the person was exposed to the infection at some point in the past. Arya’s results showed that he tested negative for the total antibody test and positive for the IgG test. “This test was useless, it gives me no concrete information. Now how am I supposed to interpret this?” Arya asked while speaking to me over the phone. Thyrocare advised Arya to take the test again a month later to get a definite result. When I emailed Thyrocare’s corporate office about the conflicting results, Dr Prachi Sinkar, the head of laboratory for Thyrocare, replied, “Results do vary depending on what is measured, after how many days of infection and also two different brands used (though all are ICMR approved). This happens in many lab tests, not just in COVID Antibodies tests.”
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