The Union Health Ministry updated its testing guidelines after it found that some states were not following up the Rapid Antigen Test (RAT) of symptomatic negative cases with RT-PCR (reverse transcription-polymerase chain reaction) tests. The Indian Council for Medical Research (ICMR) clearly states that the results of symptomatic and asymptomatic people, who test negative in the antigen test, should be confirmed with the RT-PCR test, which is the gold standard test for detecting cases of COVID-19.
In a joint statement issued on Thursday, the Union Health Ministry and ICMR wrote to all states and Union Territories, urging them to ensure that all symptomatic negative cases of RAT are mandatorily retested using the RT-PCR test. This ensures that symptomatic patients with negative antigen result do not remain untested and do not spread the disease among their contacts. “This also ensures the early detection and isolation/hospitalisation of such false negatives,” said the statement.
It has also highlighted that although the antigen test is being used to increase access and availability of testing on the field, the RT-PCR remains the gold standard of COVID tests.
An RT-PCR test will detect the presence of the genetic material or RNA (ribonucleic acid) of SARS-CoV-2 virus. An antigen test will detect the spike proteins on the virus. While an antigen test delivers results within 15 to 30 minutes, the test kits have moderate sensitivity (ability to detect true positives) — reportedly about 50% accuracy — and high specificity (ability to detect true negatives).
In July, high rates of false negatives after antigen test were reported in Mumbai. Over 60% of symptomatic patients, who showed negative with rapid antigen testing, subsequently tested positive after RT-PCR testing.
The Union Health Ministry has also urged the states and Union Territories to establish a monitoring mechanism (a designated officer or a team) in every district and to follow up on such cases at the state level.
These teams will analyse details of RATs conducted daily and ensure that there are no delays in retesting all symptomatic negative cases.
“The aim of the states and Union Territories should be to ensure that no potentially positive case is missed out. They have also been advised to undertake an analysis regularly to monitor the incidence of positives during the RT-PCR tests conducted as a follow-up,” read the statement issued by the government.
The additional advisory by the ICMR also states that the IgG test should not be used for diagnosis but only for surveillance. IgG antibodies generally start appearing after two weeks of the onset of infection, that is, once the individual has recovered after infection, and will last for several months. Therefore, the IgG test is not useful for detecting acute infection, the advisory read.