Rapid Antigen Test
- 19 Jun 2020
- Recently, the Indian Council of Medical Research (ICMR) approved the use of rapid antigen detection test in containment zones and healthcare settings in combination with the RT-PCR test.
- The ICMR has allowed the use of antigen detection kits developed by the South Korean company S D Biosensor, which has a manufacturing unit in Manesar.
- The kit, commercially called Standard Q COVID-19 Ag detection kit, comes with a with an inbuilt Covid antigen test device, viral extraction tube with viral lysis buffer and sterile swab for sample collection.
Rapid Antigen Detection Test for Covid-19
- It is a test on swabbed nasal samples that detects antigens (foreign substances that induce an immune response in the body) that are found on or within the SARS-CoV-2 virus.
- It is a point-of-care test, performed outside the conventional laboratory setting, and is used to quickly obtain a diagnostic result.
- The test has to be performed onsite under strict medical supervision and maintaining the kit temperature between 2° and 30°C.
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Rapid Antigen Test
Antigens An antigen is any substance that causes your immune system to produce antibodies against it. An antigen may be a substance from the environment, such as chemicals, bacteria, viruses, or pollen. Vaccines are examples of antigens in an immunogenic form, which are intentionally administered to a recipient to induce the memory function of adaptive immune system toward the antigens of the pathogen invading that recipient. |
Difference from RT-PCR Test
- Like RT-PCR, the rapid antigen detection test too seeks to detect the virus rather than the antibodies produced by the body.
- While the mechanism is different, the most significant difference between the two is time.
- RT-PCR test takes a minimum of 2-5 hours including the time taken for sample transportation. These specifications limit the widespread use of the RT-PCR test and also impede quick augmentation of testing capacity in various containment zones and hospital settings.
- In a reliable rapid antigen detection test, the maximum duration for interpreting a positive or negative test is 30 minutes.
Accuracy of Rapid Antigen Test
- The results revealed that the kit had a very high specificity, or the ability to detect true negatives, ranging between 99.3% and 100% at the two sites.
- The sensitivity of the test, or its ability to detect true positives, ranged between 50.6% and 84%, depending upon the viral load of the patient.
- The higher the ability to detect true negatives, the more reliable is any positive result.
- A negative test result may occur if the level of an extracted antigen in a specimen is below the sensitivity of the test or if a poor quality specimen is obtained
- A negative result may also occur if the concentration of antigen in a specimen is below the detection limit of the test or if the specimen.
- Also, children tend to shed the virus for longer periods than adults, which may result in differences in sensitivity between adults and children.
Limitations
- Antigen tests are very specific for the virus, but are not as sensitive as molecular PCR tests.This means that positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection.
- With this in mind, negative results from an antigen test may need to be confirmed with a PCR test prior to making treatment decisions or to prevent the possible spread of the virus due to a false negative.
- Further, once the sample is collected in the extraction buffer, it is stable only for one hour.
- Therefore, the antigen test needs to be conducted at the site of sample collection in the healthcare setting.
