performance of low-dose chest ct scan for initial triage of covid-19

Background: chest computed tomography (ct) scan is frequently used for diagnosis of coronavirus disease 2019 (covid19), especially in regions with limited availability of reversetranscription polymerase chain reaction test (rtpcr) test. lowdose ct of chest offers acceptable image quality with lower radiation dose, particularly important in younger patients. objectives: we have designed the current study to evaluate the diagnostic efficacy of lowdose chest ct versus early rtpcr results, for triage of covid19 patients. patients and methods: from february 20 to april 15, 2020, 163 patients including 100 males (61.3%) with the median age of 65 years (21 to 97), who underwent both rtpcr and chest ct were registered in the study. lowdose chest ct protocol was applied with parameters modified from the lung cancer screening protocol. the accuracy of lowdose chest ct for covid19 diagnosis was evaluated, considering first rtpcr results as reference. results: of 163 patients, 89 cases (54.6%) were presented with positive initial rtpcr result. lymphocyte percentage and lymphocyte count were significantly lower in the positive rtpcr group (15% versus 19%, and 0.98 vs. 1.3, respectively); while, erythrocyte sedimentation rate (esr) was significantly higher (53 vs. 22). positive chest ct findings were present in 133/163 cases (81.6%). the sensitivity, specificity, positive and negative predictive values (ppv and npv) and accuracy of lowdose chest ct scan were 96.6% (95% confidence interval [ci], 90% 99%), 36.5% (95% ci, 26% 49%), 64.7% (95% ci, 56% 73%), 90% (95% ci, 72% 97%) and 69.3% (95% ci, 61% 76%), respectively based on positive rtpcr results. conclusion: lowdose chest ct scan provides both high sensitivity and negative predictive value in diagnosing covid19 compared to initial rtpcr as the gold standard. it can be used as an alternate to standarddose ct scan in areas with high prevalence of covid19 disease and limited availability of rtpcr for early triage.