Antibodies are protective proteins produced by our immune system to protect the body from foreign substances known as Antigen in response to infection and remove them from the body. A patient shows symptoms after 5 days of infection [ incubation period 5-14 days].
There are two types of covid 19 tests: 1] Antigen test 2] Antibody test
1] ANTIGEN TEST: there are two types of antigen tests
a] Rapid antigen test: Usually, these tests are done on blood, serum, or plasma and gives rapid results within 30 minutes and test positive after 7- 10 days of infection. However NEGATIVE TEST result does not rule out covid-19 infection and requires RT-PCR TEST for confirmation. These tests are not recommended for diagnosis by ICMR.
b] RT-PCR TEST: Reverse transcriptase-polymerase chain reaction usually takes samples from nose and throat swabs. It copies and amplifies genetic fragments of the virus. It is the GOLD STANDARD frontline test for diagnosis and is usually the recommended test. Test results come after 24 to 48 hours.
2] ANTIBODY TEST
This test shows if the immune system had encountered the virus. The antibodies take 2-3 weeks after covid infection had set in and when the person is in the recovery phase.
IgM ANTIBODIES show up early in the infection phase
IgG ANTIBODIES show up later after infection.
TOTAL ANTIBODY TEST tests both IGM & IGG and comes positive early in infection
IgG ANTIBODIES come 2-3 weeks later and should be the TEST OF CHOICE to see if you have developed some immunity to the virus, however, these antibodies remain 60-90 days in the body then levels fall but they transfer some memory to T memory cells of the body to recognize similar virus attacks in future.
However POSITIVE ANTIBODY TEST does not mean that repeat covid virus infection won't take place. It shows that u have encountered the virus and got infected and developed some immunity against it. HAND HYGIENE, MASK, GLOVES EYEWEAR, PHYSICAL DISTANCING ARE STILL REQUIRED even if you have a positive antibody test.
TEST OF CHOICE SHOULD BE IgG ANTIBODIES rather than total antibody test which will be positive due to IgM early in infection.
ANTIBODY TEST IS NOT RECOMMENDED IN EARLY INFECTION.