COVID-19 Infection Immunity Test (Covid-19 Antibody Level Test) is a test to detect the amount of IgG, IgM (Total antibody) antibodies in the body against the SARS-CoV2 virus. It is also part of the immune system (Antibody) testing after receiving the COVID vaccine.
Who should get tested for COVID-19 infection immunity?
- Those who want to know the antibody levels in response to vaccination or after infection
- Those who want to know the neutralizing ability of antibodies against the COVID-19 virus
There are 2 types of COVID-19 infection immunity tests
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Binding antibody test (Bab)
This antibody is produced by the body from infection or vaccination. It specifically binds between the antibody and the virus antigen to stimulate the immune system, such as white blood cells, to eliminate the virus. However, it cannot inhibit the virus from entering cells and replicating. This test is divided into 3 types of antibody test kits:
- Rapid antibody test, known as the rapid antibody detection kit
- Enzyme Linked Immunosorbent Assay (ELISA)
- Chemiluminescence immunoassay (CLIA)
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COVID-19 Neutralizing Antibody Level Test (SARS-CoV Neutralizing Antibody: Nab)
This is a total antibody immunity test that has the ability to inhibit the virus from entering cells. Therefore, it is a complex method requiring experts in cell and virus culture. However, it is the appropriate and standard method for testing vaccine efficacy because it can indicate whether the vaccine recipient has immunity to prevent SARS-CoV-2 infection or not. It is also approved by the FDA and Thai FDA. The test result turnaround time is approximately 3 working days.
Generally, immunity in infected individuals increases to a detectable level 5-7 days or longer after symptoms appear. However, for the novel SARS-CoV-2 virus, data on immune response including IgA, IgG, and IgM types and the time antibody levels increase after infection is still limited. Current data shows most patients develop detectable immunity between 10-21 days from symptom onset. In mild cases, antibodies may be detected after 3 weeks of symptoms. For vaccinated individuals, it is recommended to have blood drawn to check antibody response 14-28 days after completing the vaccine dose, but not longer than 3 months.
