Immunity Tests – A Guide to Past Infection

Antibody tests or immunity tests help to detect the past infection from a disease. The same is also true for past infection from COVID-19.

“Your health is an investment not an expense.” You might have heard of this earlier but do you really put this to work? Pandemic phase requires regular checks on our health. Antibody Test is one such essential requirement.

When an antigen enters your body, your immune system detects them. Subsequently, the immune system produces antibodies, a special type of protein molecule. These destroy the antigen, clearing the infection. Once we recover from a disease, our body remembers these antigens and if we are attacked again, our body rapidly produces similar antibodies and removes the antigens.

Types Of Antibodies

These are also knowns as immunity test. A human body produces 5 different types of antibodies. This includes-:

• IgG
• IgM
• IgE
• IgD
• IgA

Each of these antibodies has a different function and characteristic. The heaviness of chain distinguishes these antibodies. Antibody tests help keep in account the proper functioning of these antibodies.

What do Immunity Test Tell Us?

Antibody tests inform the test taker about the presence of two most commonly produced antibodies namely IgM and IgG. Antibody tests help us know if anybody has had any infection in the past.

Antibodies do not appear until someone has had an infection for the past several days. Having an antibody, at the same time, does not always guarantee immunity against an antigen. What is important here is its effectiveness and quantity.

What Immunity Tests Detect?

These Antibody tests provide result under the following subheadings-

1. Whether one had an infection or not.
2. The infection is at an early stage or has reached a higher stage.
3. The patient has overcome the infection or is it still present.
4. Lastly, it tells about past infections.

Immunity test Vs Diagnostic Test

A diagnostic test helps in detection of present infection whereas an antibody or immunity test detects the past infection. Thus, their methods of testing also differ. For example, RT-PCR method is used for COVID -19 diagnostic test while the CMIA or ELISA or CLIA method is used for an antibody test.

When to get tested

Development and detection of antibodies depend on the disease or virus. Some of the factors which govern the timings are

• The incubation period of the virus
• Recovery period
• Post recovery drop in the antibody levels

For, COVID-19, studies have shown that it is best to get a test after 14 days of infection.

Antibody tests results

The results from antibody tests shown the level of the antibodies in our bodies. This level is compared to a standard established for a particular disease. Thus positive or negative results are established.

Accuracy Of Immunity Tests

Immunity tests Conducted in peoples’ blood might show whether they currently have an infection or had faced it previously. The accuracy of these tests depends upon false-negative and false-positive results so produced.

False-negative test results basically mean that one has a negative result that is one has antibodies against an antigen and false-positive mean that one has positive results that is one lacks antibodies against an antigen.

Just like any other test, these tests are too measured on sensitivity and specificity.

Sensitivity measures the absolute production of positive results. Imagine we have ten patients, who all have antibodies to the antigen. A test with 100% sensitivity would correctly identify antibodies in samples from all these patients.

Specificity measures the absolute production of negative results. Imagine our ten patients again; this time, none of them have antibodies to the antigen. A test with 100% specificity would correctly give negative results for all these patients.

Antibody Tests and Covid-19

Sometimes, people having corona do not always show symptoms due to several reasons. The COVID Antibody tests do not diagnose Covid-19, it simply tells whether the person had corona in the past or not. Whether a person was infected or not is revealed through these tests.

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Positive results in the antibody test of a person imply that he/she has successfully recovered from the disease. This basically proves that the person has good immunity and can easily deal with a similar virus in future. Also, the plasma of these people is useful in plasma therapy.

Let me know in case you have any questions related to antibody or immunity test. We will try to answer those in the comments section.

Reference

https://www.thermofisher.com/in/en/home/life-science/antibodies/antibodies-learning-center/antibodies-resource-library/antibody-methods/immunoglobulin-structure-classes.html