How to know the right form of serology test to recognize Covid-19 immunity?
Serology tests do not detect the presence of the virus, but rather the antibodies formed or created by the body in the battle against the disease.
If someone becomes infected with a virus, such as SAR-CoV-2, his or her body responds with an immune response by forming antibodies. These antibodies attack the virus and expel the virus from the system. If someone gets in contact with the COVID-19 but has no symptoms, tests on the antibody, sometimes called serology tests, will tell us if someone has been infected and has an immune response in the past.
Serology tests do not detect the presence of the virus but instead detect antibodies formed by or against the disease by the body.
Antibodies are proteins formed by the immune system and are unique to the particular infection in response to infection. It is contained in the liquid blood segment known as serum or plasma.
Immunoglobulin M, or IgM, is the first type of antibody that is produced for infection and can be identified 4 to 7 days after the beginning of an infection. IgM antibodies are short-lived and have symptoms of a new infection.
Antibodies of immunoglobulin G, or IgG, are formed from 7 to 14 days following infection. Depending on the antigen and the organism, these antibodies can be identified for weeks, months, and even years. IgG antibodies typically last longer and may play a role in permanent immunity. We don’t know anything about SARS-CoV-2 because it’s a new virus, but, how immunity from this virus functions we don’t know.
Total tests, which are a mixture of IgG-IgM tests, cannot differentiate early IgM from late IgG tests. Total tests cannot, therefore, decide whether a person has the IgG antibodies required for long-term immunity, or is currently infected.
The Total Antibody Test is intended to help recognize persons who have a SARS-CoV-2 adaptive immune response suggesting recent or previous infections. IgG and IgM SARS-CoV-2 antibodies are normally detected in the blood after initial infection, but they do not adequately describe the period of time during which antibodies are present post-infection.
Analysis has shown that serious and critical cases have higher than mild IgM levels, while in critical cases IgG levels were lower than in mild and severe cases. This may be due to the high activity of the disease and/or an impaired response in severe cases. In deceased patients, the levels of IgM antibodies were marginally higher than in recovered patients but the levels of IgG in both groups were not substantially different.
Longitudinal antibody detection showed that IgM levels decreased rapidly in regenerated patients while IgM levels remained elevated in deceased cases or the IgM and IgG levels were undetectable in the course of the disease.
The right type of serology test could help us to understand person and population levels of COVID19 immunity. This can be a vital method for us to build strategies for reopening society.
How to test serological IGg antibody response diagnostic output in COVID patients
Many studies, particularly in the earlier stages of COVID-19 disease, showed a limited clinical sensitivity to the IgG test. IgG testing is not appropriate for acute disease lab diagnosis but is considered for epidemiological retrospective testing. While high technical precision has been demonstrated, the IgG testing constraints should be known for clinicians to interpret the results
Reasonable sensitivity and specificity thresholds depend on the intent of the antibody test and must be considered before implementation. High sensitivity (usually up to 90 percent) is needed for diagnosis in symptomatic patients.
However, the use of antibody tests as an individual method to warn release from social isolation and to return to normal activities would require a high degree of precision because false-positive results would result in a risk of exposure for non-immune persons. Different studies have demonstrated 93.1 percent sensitivity and 99.2 percent specificities in IgG tests. This shows that the test is appropriate to determine prior exposure to viruses.
IgG tests can be used for retrospective detection of patients after 14 days after the onset of the disease. However, the interpretation of the IgG test can shift as more patients produce baseline virus antibodies. In vaccine production, clinical trials, and epidemiological research, SARS-CoV-2 IgG testing will also be instrumental.