E-Paper
Is RT-PCR test giving false negative reports because of mutants? Expert answers
It is possible that a covid positive person may test negative in an RT-PCR test, but the double mutant strain is not the reason, Dr Anurag Agarwal has said.
Amid rising Covid-19 tests, a long wait for RT-PCR tests and the results, concerns over false negative reports are being expressed. It is being speculated that because of the new mutant strains, RT-PCR tests are coming negative, even when a person is actually positive and has symptoms of the infection.
Allaying such fears, Dr Anurag Agarwal, director of the National Institute of Biomedical Genomics confirmed that while it is possible that a covid positive person may test negative in an RT-PCR test, double mutant strain is not the reason.
"Double mutant was sequenced through PCR positive. So it is not possible that the mutant escapes the RT-PCR test. Then we could not have sequenced it," Dr Agarwal said in a video, tweeted by the Union health ministry.
"All possible sequences in the world are being checked regularly and there is no strain which can escape the double gene testing," he said.
What people should remember is that PCR has a sensitivity of 70 per cent. "The load of the virus in one's mouth and nose remains the highest a day before the symptoms start showing. Then the virus load gradually decreases. If people get tested late after 7 to 8 days, it is possible to get a negative test report because the virus may have travelled inside the body," he said.
Tests coming negative despite symptoms being present is not new and not because of any new strain. This was the case since the beginning, that if delays testing, the test results may come negative, Dr Agarwal said.
RT-PCR (Reverse transcription- Polymerase chain reaction) tests are considered the gold standard in the detection of Covid-19 and that is why the Centre is asking all states to increase the percentage of RT-PCR testing, but its sensitivity is not beyond 70 per cent if all tests being done are taken into account.
Double mutant is a new strain formed by two mutated strains. In India, its presence has been found in many states, including Maharashtra and Delhi. E484Q and L452R strains have formed the double mutant.
