The ICMR invited bids for an estimated 10 lakh antibody kits (for serological tests) for the diagnosis of COVID-19.

What are serological tests?

• Viral infections are mainly identified by two kinds of tests– genetic and serological.
• Genetic tests can identify infections that are active but cannot be used to detect past infections.
• To trace how infections like the novel coronavirus have spread so far, it is important to detect people who contracted the disease in the past and have recovered.
• This is what serological tests seek to determine.

How are the two different?

• The genetic test is conducted on a swab collected from the back of the throat, a liquid sample from the lower respiratory tract, or a simple saliva sample.
• For SARS-COV-2, the virus’s RNA is first converted into DNA.
• By a process called polymerase chain reaction (PCR), DNA fragments in the sample are copied exponentially — one is copied into two, the two are copied into four, and so on.
• Unlike genetic tests, which look for RNA in swab samples, serological tests work on antibodies in blood samples. Hence, they are also called ‘antibody tests’.

How serological tests work?

• Antibodies, or protective proteins produced by the immune system to neutralize pathogens such as bacteria and viruses, are present in one’s bloodstream for a considerable period of time after the infection has gone.
• To disable a pathogen, the antibody latches to a unique protein molecule on pathogen’s surface, called an antigen.
• Serological tests use antigen molecules to detect the presence of antibodies relevant to the infection.
• Generally, a blood sample is placed in a test tube that is lined with antigens on the inside. If the relevant antibodies are present, they latch on to the antigens.
• Such tests are relatively inexpensive, and can display results within a few minutes.

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