Do CT scans detect COVID-19 better than RT-PCR tests?

Do CT scans detect COVID-19 better than RT-PCR tests?

Covid being a respiratory disease, imaging of lungs in CT gives good findings, say doctors

Published: 14th August 2020 04:15 AM |

By Sowmya Mani

Express News Service

TIRUCHY: More COVID-19 cases could be detected with a CT scan of the chest than through RT-PCR tests, claims a section of doctors in Tiruchy city. Dr Mohamed Hakkim, an emergency physician, explained the rationale. “Covid is a respiratory disease and affects the lungs, Imaging of lungs done in a CT gives a very good finding, PCR test help only if the virus is in the nose or throat.

In a CT, we can see the extent of damage clearly once the virus infects the lungs.” Sources said there have been instances where PCR tests came out negative but patinets were confirmed Covid positive through CT scan. A senior doctor in MGMGH said 70 cases were detected through RT-PCR, 100 were being detected through HRCT. Dr K Govindaraj, Director of Dr G Vishwanathan Specialty Hospitals added, “A CT scan is very sensitive. Lately, we have seen several cases of CT positive but PCR negative cases. RT-PCR would be able to detect infection from day 1 to 8.

From Day 4 of the infection to 2 weeks, a CT scan is more sensitive, even later, if the patient is symptomatic,” Another reason cited is mutation of the virus. Doctors point out that CT scan gives result in 15 minutes, while it takes at least 24 hours for PCR results. Radiologists claim PCR had 70 to 80 per cent efficiency. “We are seeing at least 10 per cent of people coming in for HRCT showing signs of Covid. CT can usually detect Covid after day 5 of infection.

There can be errors due to sampling time,” said Dr Bavaharan, Founder of Magnum Imaging and diagnostics. Radiologists follow an index called CO-RADS to confirm the severity of infection. “The level of infection is graded from very low or CO-RADS 1 to CO-RADS 6. CO-RADS 4 is suspicious for Covid and 5 and 6 are typical Covid-19,” Dr Hakkim added.

Private practitioners said because there were chances of PCR results coming negative, many infected cases could go undetected. “As per the ICMR guidelines, only RT-PCR positive cases are reported as Covid. We have double the number of patients who tested positive through CT but are not reported,” said a doctor.