Do you know about the rapid antigen detection test for COVID-19?
The first antigen-based testing kit for COVID-19 has been recommended by the Indian Council of Medical Research (ICMR) to enable faster diagnosis at lower rates and without laboratory examinations of samples.
As we know that COVID-19 cases are increasing day by day and therefore to deal with the coronavirus infections, a Korean company's antigen test kit has been validated by the ICMR that gives result in 30 minutes. A firm namely SD Biosensor will produce the kit which has a manufacturing unit in Manesar, Gurugram that can also be used in field settings.
How is the rapid antigen detection test done for COVID-19?
This is a new category of tests for use in the ongoing pandemic. These tests quickly detect fragments of proteins found on or within the virus by testing the samples collected from the nasal cavity using swabs.
The kit consists of an inbuilt COVID antigen test device, viral extraction tube with viral lysis buffer and sterile slab for sample collection. The antigen test needs a nasal swab. The swab is collected by using the customised sample collection swab provided along with the kit. According to ICMR, the test is conducted on the sample of a nasal swab and it checks the presence of antigens that are foreign substances which induce an immune response in people. It will help to determine quickly whether a person has or had the infection and is performed outside the conventional laboratory.
Further, if the test result of the antigen test is positive then it can be considered as a confirmation of the infection but if it shows negative result then according to ICMR an RT-PCR test also be done to find out the infection. According to Dr. LK Sharma, Scientist and Media Coordinator ICMR, a positive test in antigen is considered as a true positive and does not need reconfirmation by RT-PCR test. It will tell us whether the patient is infected or not.
Let us tell you that currently, RT-PCR test is the gold standard frontline test for the diagnosis of COVID-19.
What is the difference between RT-PCR test and rapid antigen detection test?
The main difference between the two is time. While the mechanism is different but the time taken in both the tests matters. As per ICMR, RT-PCR test takes minimum 2 to 5 hours including the time taken for sample transportation and in rapid antigen detection test, the maximum duration for interpreting a positive or negative test is 30 minutes.
Who authorised the first antigen test?
For COVID-19 very few antigen detection kits are available worldwide. The US Food and Drug Administration authorised the first antigen test on 9 May with the US-based Quidel's antigen kit known as Sofia 2 SARS Antigen FIA.
Japan Ministry of Health, Labour and Welfare on 14 May approved the use of Tokyo-based Fujirebio Inc.'s antigen test kit. Even in India, the ICMR conducted an independent two site evaluation of the SD Biosensor kit, at ICMR and AIIMS.
According to the ICMR, the accuracy of the kit in detecting true negatives is between 99.3% to 100% based on the validation done at two sites. The sensitivity of the kit or the rate of detecting infections correctly ranged from 50.6% to 84% which is based on two independent evaluations. The patient's viral load also matters that are higher viral load correlated with higher sensitivity.
Where the test will be conducted?
In the containment zones or hotspots and healthcare settings, the kit will be used as per the current scenario. As per guidelines issued by the ICMR, the test will be performed onsite under the strict medical supervision and maintaining the kit temperature between 2o to 30o C. The rapid antigen test will be used to test symptomatic persons. Further Asymptomatic direct and high-risk contacts with co-morbidities like lung disease, a heart condition, liver-related issues, renal disorder, diabetes, neurological disorders, blood disorders of a confirmed case are to be tested once between 5th day and 10th day of coming into contact.
In healthcare settings according to ICMR, all symptomatic patients with influenza-like illness, patients undergoing chemotherapy, patients with malignant disease and elderly patients can be tested using this kit.
Limitations of the antigen test’s results
A per US FDA, the test of antigen is very specific for the virus but are not as sensitive as molecular PCR tests. That is the positive test results from the antigen tests are highly accurate, but there is a higher chance of false-negative results. Therefore, negative results can't rule out infection. So, a negative result may need to be confirmed with a PCR test before making treatment decisions or to prevent the spread of COVID-19 due to a false negative.
Therefore, we can say that an antigen test will play an important role in the fight against COVID-19.