Covid 19 Rapid Antigen Test Kit

August 15, 2021

Antibody tests are useful to help track the spread of a contagious disease , disease that is readily spread. It can be very useful to identify those who should be vaccinated urgently, and to select the donors for convalescent plasma therapy.

Antigens are molecules capable of stimulating or encouraging an immune system response. Each antigen has distinct surface features or structures called epitopes, generating specific responses.

What are Antibody and Antigen ?

An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and remove foreign objects such as pathogenic bacteria and viruses. These antibodies are produced by B cells of the immune system due to exposure to antigens. Each antibody contains a paratope which recognizes a specific 'epitope' on an antigen, acting like a lock and key binding mechanism. This binding makes possible to eliminate antigens from the body, either by direct neutralization or by ‘tagging or labeling’ for other arms of the immune system.

Utilizing Antibodies and Antigens in Diagnostics

When infected with a pathogen (virus or bacteria) such as SARS-CoV-2, the immune system of body produces antibodies that bind specifically to the antigens to make it possible to eliminate or neutralize the pathogen. This binding can be used to develop antibody and antigen-based diagnostic tests.

An antibody test reveals that a person has already been exposed to an infection means infected, by detecting antibodies in their blood or serum, which is a fluid and solute component of blood. This can be done by a laboratory based test such as an ELISA (Enzyme-Linked Immunosorbent Assay) or CIA (chemiluminescent immunoassay), or a point-of-care test based on lateral flow technology such as LFIA or LFA.

Antibody tests are not recommended to diagnose current infection as it takes the body some time to produce antibodies. During the period before the adaptive immune system starts its response, the fast-acting and non-specific innate immune or natural immune system response combats infection. A negative test result is possible if the test is taken too early after infection before antibodies have been produced by the body. False positive test results could also occur due to cross-reactivity, which the ability of an antigen to bind with an antibody that was raised to a different antigen.

An antigen test shows a result if a person is currently infected with a pathogen. After the infection has gone, the antigen disappears. So this test can not be done at that stage.

Unlike nucleic acid (DNA AND RNA) based tests such as PCR (Polymerase chain reaction), which detect the presence of genetic material, antigen tests detect proteins, such as those found on the surface of a virus. Accuracy can be a problem, with antigen tests having a much lower sensitivity than PCR.

However, they usually provide test results rapidly, and low cost, and can be more done at a point-of-care location, which could make them more suitable for testing at the airports or bus stations and in remote regions.