Diagnostic accuracy of ultra-low-dose chest CT vs chest X-ray for acute non-traumatic pulmonary diseases.

Objectives: To compare the diagnostic accuracy of ULDCT to CXR for detecting non-traumatic pulmonary diseases at the emergency department (ED) and to study diagnostic confidence levels.

Methods: Secondary analysis of the prospective OPTIMACT trial (2418 ED participants randomly allocated to ULDCT or CXR). Diagnoses at imaging at the ED were compared to the reference diagnosis on day 28. Ratios of positive diagnoses, true positives (TP), false positives (FP), false negatives (FN), and positive predictive values (PPV) were assessed with 95% confidence intervals (CI). The diagnostic confidence levels of the radiologists were studied.

Results: One thousand one hundred sixty-one ULDCT participants (mean age, 59 years ± 18 [standard deviation], 587 female) and 1151 CXR participants (mean age, 59 years ± 18 [standard deviation], 561 female) were evaluated. With ULDCT, pneumonia was 1.55 times (95% CI: 1.33-1.80) more often diagnosed at imaging at the ED, with significantly more TP (ratio 1.50; 95% CI: 1.26-1.76) and fewer FN (0.61; 95% CI: 0.37-0.99) but more FP (1.75; 95% CI: 1.19-2.58); a similar pattern was observed for other lower respiratory tract infections (LRTI). Pulmonary congestion was less often observed with ULDCT (0.45; 95% CI: 0.34-0.61), with fewer TP (0.50; 95% CI: 0.34-0.73), and FP (0.40; 95% CI: 0.24-0.65). PPVs were not significantly different. With ULDCT, radiologists were more often certain in diagnosing pneumonia (ULDCT 121/324, 37% vs CXR 48/208, 23%), LRTI (84/192, 44% vs 18/63, 29%), and no established disease (350/382, 92% vs 447/544, 82%).

Conclusion: Compared to CXR, ULDCT led to more TP but also more FP in detecting pneumonia and LRTI, while fewer TP and FP were found for pulmonary congestion. PPVs were comparable.

Key Points: Question Is ultra-low dose CT (ULDCT) more accurate than chest X-ray (CXR) for identifying non-traumatic pulmonary diseases in patients presenting at the ED? Findings ULDCT detects more pulmonary infections in patients presenting at the ED with non-traumatic pulmonary complaints, while CXR detects more pulmonary congestion. Clinical relevance ULDCT is superior to CXR in detecting pneumonia and other LRTI in ED patients, while CXR is superior in detecting pulmonary congestion. ULDCT can be an alternative for CXR in a selected group of patients.