New Delhi’s approach to testing for Covid-19 has recently drawn criticism due to the minimal re-testing of persons who tested negative in Rapid Antigen Detection Tests (RADT). Critics argue that the widespread use of RADT without sufficient follow-up retests contradicts the guidelines set by the Indian Council of Medical Research (ICMR) for RADT usage.
ICMR Guidelines on RADT Usage
According to the ICMR, RADT should primarily be used in containment zones, hotspots, hospitals, and laboratories, among individuals exhibiting symptoms associated with Covid-19, such as influenza-like illnesses. The guidelines also extend to asymptomatic individuals with co-existing health conditions, and those with high-risk contact with confirmed positive cases. If clinicians suspect a ‘negative’ test result may be inaccurate, a sequential RT-PCR (Reverse Transcription Polymerase Chain Reaction) test is necessary to rule out infection and higher chances of false negatives. However, re-testing is not required for those who test positive in RADT.
Covid-19 Testing in New Delhi
Between 18th June and 16th July, New Delhi conducted 3,05,820 RADT. Out of these, 2,85,225 tests returned ‘negative,’ but only 1,670 of these were selected for an RT-PCR retest. Of these retests, 262 tested positive. This means that only one in every 200 individuals who tested negative in the antigen test were retested despite ICMR guidelines, indicating the possibility of under-reported infection rates.
Arguments for Limited Retests
Some argue that retesting everyone would undermine the purpose of the rapid antigen test. Since an RT-PCR test takes a minimum of 2-5 hours, including transport time for samples, it isn’t viable for widespread use and can hinder the rapid augmentation of testing capacity in containment zones and hospitals. RADT, on the other hand, provides results within 30 minutes, making it a quicker alternative to RT-PCR.
Drawbacks of Insufficient Re-testing
If RADT is indiscriminately used, it could inflate the overall testing numbers while not accurately reflecting the extent of the virus’s spread among the population. The low level of re-testing with RT-PCR for those who test negative in the antigen tests could also lead to underestimating case numbers and inaccurate virus tracking.
About RADT
The Rapid Antigen Detection Test uses nasal swab samples to detect antigens (foreign substances that induce an immune response) found within the SARS-CoV-2 virus. It’s a point-of-care test done outside conventional labs and quickly produces diagnostic results. Unlike the RT-PCR test, RADT aims to detect the virus, not the antibodies produced by the body, and gives results in 30 minutes.
About RT-PCR Test
The RT-PCR technique was invented by American biochemist Kary Mullis, who received the Nobel Prize for Chemistry for his efforts in 1993. This test involves creating copies of a DNA segment using an enzyme called Polymerase, shown by a fluorescent DNA binding dye added to the DNA. As coronavirus is made of RNA, it is converted into DNA using a method called reverse transcription to be detected. An enzyme called ‘reverse transcriptase’ accomplishes this conversion, after which the DNA copies are amplified.
Last Modified: February 8, 2024