Use of CT Angiography in a Country with Low Pulmonary Embolism Prevalence: Correlation with Clinical Pretest Probability and D-dimer Values

To assess the use of CT angiography (CTA) in the diagnostic evaluation of pulmonary thromboembolism (PE) in a country with low PE prevalence and correlate the diagnostic performance of CTA with the clinical pretest probability and D-dimer values. The institutional review board approved this retrospective study. The observers reviewed all 660 CTAs and calculated the PE clot burden scores. The pretest probability of PE according to the Wells criteria and D-dimer values were calculated (clinical data were available for 371 of the 660 patients). We correlated the PE positivity rates of CTA and a PE clot burden score with the D-dimer values and pretest probability using Pearson's correlation coefficient. Of the 371 patients whose clinical data were available, 122 (32.8%) had PEs. None of the patients with both a normal D-dimer value and a low clinical probability had a PE. PE positivity rates of CTA were correlated with clinical pretest probability (r = 0.164, p = 0.002) and D-dimer values (r = 0.361, p < 0.001). PE clot burden scores were correlated with D-dimer values (r = 0.296, p < 0.001). Although PE positivity rates of CTA in a country with low prevalence were higher than those in a country with a higher prevalence, approximately 30% of the yield still represents an overuse of CTA. CTA should be performed after the pretest probability has been assigned and if the result of a D-dimer assay is abnormal.