A serological survey includes IgG Enzyme Linked Immunosorbent Assay (ELISA) test. It estimates the proportion of the population exposed to Sars-Cov-2 infection.
The IgG test is not useful for detecting acute infections but it indicates episodes of infections that has happened in the past. The test is approved by ICMR for its high sensitivity and specificity.
Five millilitres of blood sample is collected from the subjects and then put in a machine where blood and plasma are separated. The plasma is then used to detect antibodies developed against Covid-19 in the body.