Lung scan not substitute for RT-PCR

Tirupati: Though CT scan of chest is not a primary screening test for coronavirus, panic driven people are rushing towards scanning centres to get it done. There was a view among some doctor circles too that since Covid-19 is a respiratory disease, the chest imaging may help diagnose people for the disease. In the eagerness to know whether they are Covid positive, people are even going directly to diagnostic centres to undergo a CT-scan to know the result instantly. However, Dr Alladi Mohan, Head of Medicine Department at SVIMS, said that CT chest is not a replacement for RT-PCR. "Doctors use it not as an upfront diagnostic test but as an add-on test to know about the extent of involvement and disease severity," he said.

In an exclusive interview to The Hans India, Dr Mohan clarified that CT chest will tell 'where' the disease is though some patterns are suggestive. It will not commonly tell 'what' the disease is and as such 'will not confirm' Covid-19. To know what the disease is one must do RT-PCR.

"Taking the history of exposure, travel, symptomatology background etc., into consideration, if there is a clinical suspicion of Covid, the diagnostic test is RT-PCR only though it may be positive or negative. If it is positive and the patient could not maintain oxygen saturations then CT scan will help in severity grading," Dr Mohan explained.

It may be definitely useful when RT-PCR is negative though the patient is having known exposure to a positive patient, known work environment exposure and typical symptoms of Covid. Hence it has to be used judiciously, he added.

Also, the scanning centres are not prepared to handle Covid load as people go there inadvertently to know whether they are Covid positive, there is a danger that even a non-positive person may also get infected by undergoing the test in the same mission used for a positive person previously. In such cases, it will become hazardous to the public, he opined.

"CT will be helpful when used as a conjunction to RT-PCR and not as a replacement to it. Since it is radiation exposure it has to be used only if necessary. Even blood tests like CRP, Serum Creatinine etc., are to be interpreted in the context of infection and not as a substitute to RT-PCR," he underlined.

To a question on an audio message that is going viral in WhatsApp which says that vaccination will cause Covid positive if tested in the next 2-3 days, Dr Mohan clarified that vaccination may cause fever, but will not cause positive RT-PCR test result. Following vaccination some recipients can develop fever for 2-3 days which can respond to symptomatic treatment.

Both the available vaccines are incapable of infecting the recipient but makes the host immune system to prepare defence mechanisms.