RT-PCR still most effective for large-scale testing, says Dr Harsh Majahan

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Viruses mutate all the time and Covid-19 is no exception to the rule. Any new strain of SARS-CoV-2 can be identified by examining the genetic code from sample of an infected person. Currently,  Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) test is the most commonly used and widely trusted method to verify if a person is infected or not.

However, the introduction of a series of new strains of the virus have left many worried and doubtful on the credibility of this testing method. There are reports which claim that RT-PCR technique isn’t good enough to detect the new variants of coronavirus and a new testing method called cartridge- based nucleic acid amplification test (CB-NAAT) must replace it for credible results.

“Both RT-PCR and CB-NAAT are fundamentally the same. They are equally sensitive and specific. RT-PCR tests, contrary to popular belief, doesn’t miss out on any new mutants. CB-NAAT, which is essentially a cartridge based test, is only quicker (takes 40-45 minutes) in running the tests as compared to RT-PCR (takes 60-90 minutes). While CB-NAAT might be quicker, RT-PCR is still most effective for last scale testing,” Dr Harsh Mahajan, founder and chief radiologist, Mahajan Imaging, told Money9 in an exclusive interview.

Fast results

A major distinguishing factor about CB-NAAT is its ability to produce test results in a short timespan as compared to the gold standard testing technique – the RT-PCR.

Now, if you have a person who needs immediate hospitalisation due to sudden illness, get them tested via CB-NAAT technique and you’d know whether the person requires Covid treatment or not within an hour. This technique can come handy for people wanting to catch an immediate flight abroad and require a Covid test report to get onboard.

What are the disadvantages of CB-NAAT?

“This is an expensive test. Cartridge itself costs around Rs 2,500-Rs 3,000 which eventually increases the cost of the test. Secondly, CB-NAAT isn’t fit for mass testing – something India desperately needs at the moment. RT-PCR machines, on the other hand, can put in 97 samples in one go and churn the results within 24-48 hours,” Dr Mahajan asserted.

He also said if RT-PCR test results are taking more time than usual, it is due to the excessive case load on the labs. They are testing more samples than their everyday capacity which eventually causes a delay in final results.

People questioning the RT-PCR tests might also be a result of Covid-19 cases rising at an unprecedented pace in the country. Are enough tests being conducted in the country to detect patients at an early stage of infection? Do we have good quality testing kits in surplus?

“From barely a handful public and private testing labs in 2020, India today accounts for more than 2,400 of these. Having successfully conducted 1.6 million tests in a day, there is no question on the testing capacity within country. Ever since the pandemic hit us, there have been indigenous manufacturers who’ve made RT-PCR testing kits in India and I can assure you there is no shortage of kits, whatsoever,” he said.

But the sudden surge in positivity rate of patients has definitely left the entire testing infrastructure over-burdened. Labs across the country are working in extra shifts to overcome the unusually high testing rate and deliver in as limited time as possible.

“We have increased the number of working hours and tried to hire extra personnel to share the humongous workload that awaits our compliance. We have also tried to get additional machines from abroad to ramp up capacity. In the mean time, we’re trying our best to deliver quality results in the limited time we’ve got,” Mahajan explained.