Doctors have been witnessing a surge in cases with Covid-like symptoms, with negative Rt-PCR results despite multiple testing. To confirm Covid-19, patients are being asked to undergo C-reactive protein (CRP) tests, a blood work that reveals inflammation and infection level in the body more synonymous with other viral infections and influenza.
Senior doctors from civic-run hospitals said CRP tests are recommended these days if Rt-PCR tests are negative. A doctor, on condition of anonymity, said severe acute respiratory syndrome and influenza-like illness have co-existed with Covid-19. “Since the pandemic started, over 30 per cent of patients have shown coronavirus-like symptoms but their reports are negative. The cause can only be identified through genome sequencing,” the doctor said.
Meanwhile, Dr Mala Kaneria, a consultant at Jaslok Hospital’s department of infectious diseases, said Rt-PCR false negativity is also common and many instances of this have been noted, especially during the second wave of the pandemic.
Kaneria attributed this to errors in swab collection. These include the swab tip not going deep enough to collect a good sample, use of faulty reagents, inappropriate method of transport to the laboratory or faulty processing techniques. Other reasons include taking the test too early (in the first 5 days, when the chances of virus detection are low) or taking the test too late when the virus replication is no longer in the nose but has migrated to the lungs, especially in severe cases.
“Lower viral loads, too, may lead to false negativity,” she said.
Dr Kaneria said another reason for false negativity could be the ability of certain SARS-CoV2 variants to evade diagnostic tests. However, tests that use multiple genetic targets, like the ones in use in India, are less likely to miss the variants.
