Rapid Antigen Test, You have heard a lot about rapid covid-19 testing. It is one of the frequently used tests to carry out widespread screening. At the beginning of the pandemic, only PCR tests were available, which was about 63-98% accurate. Due to chemical reagent shortage and delay in results, a rapid antigen test was developed.
What is the Rapid Antigen Test?
Rapid antigen test (RAT) also called Rapid antigen detection test (RADT) is a new type of diagnostic test approved by the Indian Council of Medical Research (ICMR) for the fast detection of the SARS-CoV-2, virus that causes COVID-19 in patients. It directly detects the presence or absence of antigen. It generates the diagnostic results within 30 minutes. These tests are designed to identify a specific protein in the virus that affects the immune system of the body. It is a type of lateral flow test. Lateral flow tests are simple devices intended to detect the presence of a target substance in a liquid sample without the need for specialized and costly equipment.
There are four types of tests, which are discussed below
The simple rapid antigen test
This test can be done in large numbers and can be taken frequently. Thus, research shows they are critical for screening. They could be taken at home and do not require any electronic device. Each test is a simple paper strip. To make them easy to use, people could either insert them into a reusable plastic cassette, or they could use a mobile phone app to read the results.
Encased rapid antigen test
Some of the rapid tests come up with special cardboard or plastic cassette, which make them reusable. But factories require a lot of time for their assembling process. Thus, they are not enough for widespread daily testing.
Electronic device rapid testing
This type of testing provides results at a faster rate but requires an electronic device. They are more sensitive than a simple rapid test but the manufacturing complexity makes them less likely to be used frequently.
Standard PCR Test
This is a hypersensitive test and it should be done in an advanced laboratory and typically return results within 24 hours or sometimes more. Because of their cost and operational complexity, these tests cannot be performed frequently for most people. While useful for medical diagnosis, they are not the best choice for public health transmission reduction.
In addition to these tests, there is an antibody test available. This test is used for past coronavirus infections and cannot be used for diagnosing active infections.
The Rapid Antigen Test kit has been developed by the IIT Delhi researchers led by Professor Harpal Singh and his team from the Centre for Biomedical Engineering. During the pandemic period, the development of Rapid test kit diagnostics become easy and affordable for rural areas. The experts suggest that the results obtained are qualitative, which means the results can be inferred visually with the naked eye. In the test region, a SARS-CoV-2 positive specimen produces a distinct color band which is formed by the specific antibody-antigen colored conjugate complex. The absence of this colored band in the test region suggests a negative result against Covid-19. The Rapid antigen test is having many advantages over RT-PCR Test. Most importantly, the test can be performed directly at the point of care without the need for transporting samples to specialized laboratories and also the rapid availability of results. They also require less instrumentation and personal qualification and usually low cost. But it is having less sensitivity but higher specificity.
These tests closely mimic one of the earliest prototypes – the urine pregnancy test – and as a result, they have gained wide acceptance based on their overall simplicity, low cost, and relative accuracy. In some situations, especially as a screening test, they can be used instead of the more technically demanding and complex molecular and serologic assays that are still useful and helpful under many different circumstances. Antigen detection systems are based on finding a particular immunogenic component, typically a protein or polysaccharide molecule, that is both unique and an integral part of the pathogen or other biological entity. Because these tests generally provide only qualitative results, they often need to be supplemented with other and sometimes more sophisticated laboratory-based diagnostic procedures to corroborate the initial test result
Rapid antigen test usually takes 15-20 minutes, though the exact time depends on the test kit and where the test is conducted. These tests can detect COVID-19 antigens in people with symptoms or asymptomatic infections. Rapid antigen tests cannot detect infections in people who have recovered from their illness. When your body fights a virus, it uses antibodies to attack and expel the antigens, leaving nothing for this test to detect.
Testing for COVID-19 is usually conducted using one of the three methods-rapid antigen tests, rapid antibody tests, or PCR tests. While each type of test is valuable, there are distinct differences that could make one more or less effective for your purposes.PCR test that detects the virus’s genetic material and so can confirm an active infection. Antigen tests are much easier and less expensive to manufacture and simpler to perform than either PCR tests or antibody tests. The same technology is used in pregnancy tests. The procedure for the antigen test includes the collection of the sample by swabbing and rotating the cotton swab inside both nostrils, secondly placing the swab inside the testing well, then adding the liquid testing solution, and finally waiting for 15 minutes to get a result.
During the test, any SARS-CoV-2 antigens contained in the sample react with the antibody-coated nanoparticles contained in the reactive test strip. As a result, the blend migrates chromatographically by capillary action along the reactive strip. If the specimen contains SARS-CoV-2 antigens, these will bind to SARS-CoV-2 antibodies contained in the (T) Test line region and generate a colored line on the test strip, indicating a positive result.
Even though it is having some disadvantages, in the present scenario the usage of rapid antigen tests is increasing day by day.