A new research conducted by Parel-based Indian Council of Medical Research-National Institute of Research in Reproductive Health (ICMR-NIRRH) shown antigen negative tests came positive when retested with RT-PCR for 33.7% of the total samples collected.
This is a crucial part of the the state’s Covid puzzle since 60% of daily Covid-19 tests in Maharashtra are done using the rapid antigen test (RAT), preferred for ease of use and shorter turnaround time.
The study was conducted between July 7 and August 7, 2020.
The institute studied its own database of 412 antigen negative reports that were retested with RT-PCR (reverse transcription polymerase chain reaction), the gold standard test to detect coronavirus. It found that the repeat RT-PCR could pick up 139 positives (33.7%) that were missed by antigen, according to a ToI report.
Of the 139 positives, 91 (65%) were symptomatic, and 48 (27%) were asymptomatic.
The highest positivity of 45% was found in high-risk contacts followed by 12.2% among police custody individuals, 22.2% in pregnant women and 33.3% in individuals hospitalised for pre-operative or other medical conditions.
“Confirmation of antigen negative tested individuals by RT-PCR, especially for asymptomatic or high-risk groups, is critical for prompt isolation and clinical management,” the paper that was published in the Indian Journal of Medical Microbiology stated. Lead author Kiran Munne underlined that the RAT showed lower sensitivity than RT-PCR test both for symptomatic and asymptomatic infection.
The findings are significant since the extent of ‘false negatives’ is proved from data from real world settings, ToI quoted Dr Smita Mahale, co-author and former director of ICMR-NIRRH.
“People need to be educated that an antigen negative test is not a stamp of being infection-free. If the person has symptoms or is a high-risk contact, he/she must be sensitised about the need to get tested again,” she said.
The state has been carrying out an average of 2.4 lakh tests of which around 1.3 lakh are antigen tests .