ELISA antibody test for COVID-19

ELISA is short for Enzyme-linked immunosorbent assay. The test uses the basic antigen-antibody reaction to detect small amounts of antigen, antibodies, proteins, hormones and peptides (small chain of amino acids the building blocks of proteins) in a given clinical sample. 

An antigen is a protein that is produced by or is present on the surface of microbes. An antibody is a protein that is produced by our immune system against antigens (and hence the microbe).

During the test, the antigen (the part of the virus against which antibodies are formed) is immobilised in a microtiter plate and the serum of the patient is put into the plate. Any free antibodies present in the serum will bind to the antigen present in the plate and the unbound antibodies are washed off. After this, a secondary antibody is added to the plate, which then goes and binds to the first antibody on the antibody-antigen complex. The secondary antibody has an enzyme attached to its surface - usually alkaline phosphatase or glucose oxidase. When the substrate for the enzyme is put up in the plate, it creates a colour which can be seen with the naked eye. This gives a simple yes or no answer to the test - the colour will only develop if the patient’s serum had antibodies. 

The intensity of colour developed can be then used to tell the number of antibodies present in the patient’s blood. 

Read more: Who can get tested for COVID-19

ELISA is a highly sensitive and efficient test that can be used to detect small amounts of antigen (antibodies) in a sample. In the case of COVID-19, specific proteins present on the spikes of the SARS-CoV-2 virus are perceived to be the antigens for this test. Spike proteins are present on the outer coating of the viruses and help them enter into body cells. They are usually the antigens against which the human body create an antibody response.

Scientists are not sure yet which part of the spike protein is being used to enter the body. However, some researchers at the Icahn Scool of medicine have published information about using the whole (modified, so it can stay stable in labs for mass production) spike protein or only the part that binds to antibodies.

• An ELISA test can run several samples at once, hence saving time. 
• An ELISA test can tell if you have been infected with a pathogen recently or in the past - depending on the presence of antibodies in your serum.
• This test is already being used to screen for HIV/AIDS, malaria and some other diseases.
• In the case of COVID-19, ELISA test can be used to screen for immune healthcare professionals who can be put in the front line of treatment of the infected patients.
• Also, ELISA can help screen for potential plasma donors for the treatment of serious cases of COVID-19 (convalescent plasma therapy). The US Food and Drug Administration (FDA) has authorised the use of plasma for severe and life-threatening COVID-19 cases.
  The plasma can be isolated from those who have recovered from the disease and hence have antibodies against it. Plasma is a major part of the blood that constitutes mostly water, salts, enzymes and antibodies. 

Read more: RT-PCR test for COVID-19