Rapid antigen tests are commonly used in the diagnosis of respiratory pathogens, including influenza viruses and respiratory syncytial virus.
What is an antigen?
In general, antigens are composed of proteins, peptides, and polysaccharides. Any portion of bacteria or viruses, such as surface protein, coat, capsule, toxins, and cell wall, can serve as antigens, reports News-Medical.Net.
Moreover, a combination of lipid or nucleic acid with proteins or polysaccharides can form more complex antigens, such as lipopolysaccharides. Lipopolysaccharides are major ingredients of endotoxins produced by gram-negative bacteria.
An antigen contains distinct sites on its surface, which is called an epitope or antigenic determinant. Antibodies generated against an antigen recognize and interact with specific epitopes via antigen-binding sites (paratopes) to trigger immune responses.
Antigens in medical science
Pathogen-specific antigens can be used as diagnostic markers to detect the current infection status of an individual. Rapid antigen tests are immunoassays used to detect the presence of pathogen-specific proteins in biological samples.
Also, pathogen-specific antigens are used in vaccine production. During vaccine production, pathogen-specific antigens are processed so that they can induce desired immune responses without causing disease.
In tumor vaccines, tumor-specific antigens are used to trigger immune cells that specifically target and destroy cancer cells.
How does an antigen test work in Covid-19 test?
Antigen tests are well named: They look for antigens. To identify these antigens, antigen tests use antibodies.
The test can provide results within 15 minutes.
The tests for COVID-19 are fast and easy – and could solve the coronavirus testing problem despite being somewhat inaccurate
According to US Centres for Disease Control and Prevention (CDC), Antigen tests are immunoassays that detect the presence of a specific viral antigen, which implies current viral infection.
They are relatively inexpensive and can be used at the point-of-care. Devices used in the tests can return results in about 15 minutes.
Antigen tests for SARS-CoV-2 are generally less sensitive than viral tests that detect nucleic acid using reverse transcription polymerase chain reaction (RT-PCR).
Rapid antigen tests perform best when the person is tested in the early stages of infection with SARS-CoV-2 when viral load is generally highest, CDC says.
There are limited data to guide the use of rapid antigen tests as screening tests on asymptomatic persons to detect or exclude Covid-19, or to determine whether a previously confirmed case is still infectious, CDC notes.
Antigen Tests in Bangladesh
Aiming to speed up the testing process, Bangladesh has introduced the antigen-based rapid testing in 10 districts of the country today to diagnose the novel coronavirus at a free of cost.
The Health Minister Zahid Maleque virtually inaugurated the program at 10am on Saturday.
The districts are - Panchagargh, Gaibandha, Joypurhat, Patuakhali, Meherpur, Munshiganj, Brahmanbaria, Jashore, Madaripur and Sylhet.
The tests will be conducted at the sadar hospitals of nine districts and Shaheed Shamsuddin Medical College in Sylhet.
The government issued a circular on September 17 allowing antigen-based rapid testing for Covid-19 at hospitals and health institutes across Bangladesh.
On July 5, the DGHS wrote to the Health Ministry to allow antigen-based Covid-19 testing. The National Technical Advisory Committee on Covid-19 also recommended it several times.