Predictors of Positive Computed Tomography Pulmonary Angiogram Scans in Suspected Pulmonary Embolism: A Retrospective Exploratory Cohort Study

Background: The ideal diagnostic strategy for diagnosis of Pulmonary Embolism in hospitalised patients is affected by confounding factors leading to unnecessary Computerised Tomography Pulmonary angiogram (CTPA). Aim of this study was to determine the positivity rate and factors predicting a positive CTPA. Patients and Methods: This was a retrospective cross-sectional analysis of CTPAs over one year period to find CTPA yield and predictors. Results: The mean age of the population was 63.1 (± 15.29) years and 39 % were males. CTPA positivity rate was 25.3% (42 out of 165 cases). Multivariate logistic regression showed that Wells score> 4 (adjusted OR 10.85; bootstrapped 95% CI4.44 – 58.05, P = 0.001) and echocardiographic RV strain (aOR3.27; bootstrapped 95% CI 1.34 – 9.32, P = 0.006) were independent predictors of positive CTPA. D Dimer > 1000 ng/ml was also significantly associated with positive CTPA (aOR 4.25; bootstrapped 95% CI 1.46 – 385.0), P = 0.008). The multivariate model demonstrated good discrimination with an area under the Receiver Operating Curve of 0.848 (95% CI 0.788 – 0.908, P <0.001). A post-hoc analysis evaluated a combined Wells score less than 4 and negative echocardiographic RV strain identified a low-risk group with a negative predictive value of 97.2% (95% CI 90.3 – 99.7%). Conclusions: In this retrospective exploratory cohort, Wells score ≥4 and echocardiographic RV strain were independent predictors of CTPA positivity. The combination of Wells score less than 4 and no echocardiographic RV strain identified a low – prevalence subgroup with NPV 97.2%. This exploratory finding requires prospective external validation before clinical application.