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COVID-19: Parliamentary panel red flags rapid antigen tests

NEW DELHI, NOV 22 (AGENCIES) | Publish Date: 11/22/2020 11:35:12 AM IST

Parliamentary Standing Committee on Health and Family Welfare in its recent report on COVID-19 has said that it is “worried at the use of less reliable diagnostic tests which increase the chances of false negatives”.

The chairperson of the parliamentary standing committee on health, Ram Gopal Yadav, submitted the report titled, ‘Outbreak of Pandemic COVID-19 and its Management’ to Rajya Sabha chairman M Venkaiah Naidu. This is the first report by any parliamentary panel on the government’s handling of COVID-19 pandemic.

The report said that the government “must assess the veracity of Rapid Antigen Test vis-à-vis RT-PCR and other diagnostic tests…to bring forth the true picture of the testing capacity in the country”. It has “strongly recommended” that testing facilities are ramped up “for more accurate tests”.

The report also noted, “testing facility is only limited to bigger districts and cities”, and “lack of testing facilities in rural areas has also resulted in underreporting of cases”.

Rapid antigen 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. 

As per The Indian Express, the test is a point-of-care test, performed outside the conventional laboratory setting, and is used to quickly obtain a diagnostic result. As per IndiaSpend, antigen testing is faster and cheaper than the “gold standard” of testing, the RT-PCR technology. It also very accurately detects positive cases of COVID-19. But its downside is that it gives a substantial number of ‘false negatives’ where a person’s test can come as negative when they could actually be positive for the viral disease.

Difference between RT-PCR and rapid antigen test: As mentioned by the Indian Council of Medical Research (ICMR), the 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 impedes quick augmentation of testing capacity in various containment zones and hospital settings,” the ICMR advisory stated.

In a reliable rapid antigen detection test, the maximum duration for interpreting a positive or negative test is 30 minutes. As per guidelines issued by ICMR, those who test negative for COVID-19 by rapid antigen test should be definitely tested sequentially by RT-PCR to rule out infection, whereas a positive test should be considered as a true positive and does not need reconfirmation by RT-PCR test.

In a circular on 23 June, 2020, about “newer additional strategies for COVID-19 testing”, the government stated that antigen testing can help at “field level for early detection of infection and quick containment” and can give a “quick diagnosis of SARS-CoV-2 in field settings”. The government then said that this technology should be used both in field settings (outside of the laboratory) as well as in hospitals and along with the RT-PCR test technology.

The ICMR has conducted an independent two-site evaluation of the SD Biosensor kit, at ICMR and AIIMS. 

The results revealed that the kit had 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.

This means that when it returns a positive result, it is 99.3% to 100% accurate, but when it returns a negative result, it could be only 50.6% to 84% accurate.

This implies that the use of rapid tests could be letting some infected people return freely to the community, spreading the virus to even more people.

For example, in the Philippines,a high number of false negatives on tests conducted on returning workers meant that infections were seeded in new places when they were allowed to go home, sparking a fierce resurgence of cases.

Mixing up these two data points could give an impression that a state is testing widely and that its number of positive cases is falling or that the increase in case numbers is slowing, when in fact that may not be the case.

However, others also point out that even “gold standard” RT-PCR can miss infections, only to a lesser extent than RAT.

 

-Tags:#COVID-19

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