The Role of the Computed Tomography (CT) Thorax in the Diagnosis of COVID-19 for Patients Presenting with Acute Surgical Emergencies. A Single Institute Experience

The current Coronavirus disease 2019 (COVID-19) pandemic has had a huge impact on emergency surgical services in the UK. The Royal College of Surgeons (RCS) published guidelines about COVID-19 pandemic in March, 2020 to aid decision making for the surgeons. These guidelines recommended that all patients requiring urgent surgery should have reverse transcriptase polymerase chain reaction (RT-PCR) and/or computed tomography (CT) thorax pre-operatively. However, it is currently unclear whether the use of CT thorax is a sensitive and specific diagnostic test. The objective of this study was to find out whether CT thorax is a reliable and accurate test in the diagnosis of COVID-19 compared to RT-PCR. This is particularly important in surgical patients where there is no time to wait for RT-PCR results. A prospective cohort study of patients presented with acute surgical emergencies at a University Teaching Hospital was conducted. Data was collected from March 23, to May 15, 2020, during the peak of the crisis in the UK. All adult patients presented with operable general surgical emergencies were considered eligible. Another group of patients, admitted with acute medical emergencies but with suspected COVID-19 infection, was used for comparison. Data was manually collected, and sensitivity, specificity and predictive value were calculated using the MedCalc statistical software version 19.2.6. Standard reporting for COVID-19 infection for CT chest based on guidelines from British Society of Thoracic Imaging (BSTI) and Radiological Society of North America (RSNA) was used. Patients who had their CT thorax reported as typical or classic of COVID 19 (high probability) were treated as infected cases with extra precautions in the wards and surgical theatres as suggested by health and safety executive (HSE). These patients had serial RT-PCR during their admissions or in the post-operative phase, if the first swab was negative. For the study, 259 patients were considered eligible for inclusion from both groups. Patients admitted for acute surgical emergencies were treated according to RCS guidelines and subjected to RT-PCR test and/or CT scan of the thorax. There were 207 patients with high clinical suspicion of COVID-19. Of those 207 patients, 77 patients had CT thorax with radiographic features consistent with COVID-19 pneumonia. However, only 40 patients had a positive RT-PCR result. CT thorax was normal in 130 patients, out of which 29 patients were found to have COVID-19 diagnosis after swab test. Sensitivity of CT scan to diagnose COVID-19 infection was found to be 58% (95% CI; 45.48% to 69.76%) whilst specificity was 73% (95% CI; 64.99% to 80.37%) with a negative predictive value of 77.69% (95% CI; 72.17% to 82.39%). CT scan was found to be a reliable tool in the diagnosis of COVID-19. With a negative predictive value of up to 82.4%, CT thorax can play an important role to help surgeons in their decision making for asymptomatic suspected cases of COVID-19. However, over-reliance on CT scan which also has a high false positive rate for diagnosis of COVID-19 infections can lead to overtreatment, overuse of resources and delays in decision-making process. Hence, results should be interpreted with caution and correlated with clinical presentation and swab test results.