OBJECTIVE: Our objective was to evaluate the diagnostic value of computed 
tomography angiography (CTA) and ventilation perfusion (V/Q) scan in the 
assessment of pulmonary embolism (PE) by means of a Bayesian statistical model.
METHODS: Wells criteria defined pretest probability. Sensitivity and specificity 
of CTA and V/Q scan for PE were derived from pooled meta-analysis data. 
Likelihood ratios calculated for CTA and V/Q were inserted in the nomogram. 
Absolute (ADG) and relative diagnostic gains (RDG) were analyzed comparing post- 
and pretest probability. Comparative gain difference was calculated for CTA ADG 
over V/Q scan integrating ANOVA p value set at 0.05.
RESULTS: The sensitivity for CT was 86.0% (95% CI: 80.2%, 92.1%) and specificity 
of 93.7% (95% CI: 91.1%, 96.3%). The V/Q scan yielded a sensitivity of 96% (95% 
CI: 95%, 97%) and a specificity of 97% (95% CI: 96%, 98%). Bayes nomogram 
results for CTA were low risk and yielded a posttest probability of 71.1%, an 
ADG of 56.1%, and an RDG of 374%, moderate-risk posttest probability was 85.1%, 
an ADG of 56.1%, and an RDG of 193.4%, and high-risk posttest probability was 
95.2%, an ADG of 36.2%, and an RDG of 61.35%. The comparative gain difference 
for low-risk population was 46.1%; in moderate-risk 41.6%; and in high-risk a 
22.1% superiority. ANOVA analysis for LR+ and LR- showed no significant 
difference (p = 0.8745, p = 0.9841 respectively).
CONCLUSIONS: This Bayesian model demonstrated a superiority of CTA when compared 
to V/Q scan for the diagnosis of pulmonary embolism. Low-risk patients are 
recognized to have a superior overall comparative gain favoring CTA.