Does a clinical decision rule using D-dimer level improve the yield of pulmonary CT angiography?

OBJECTIVE: The objective of our study was to evaluate the impact of incorporating a mandatory clinical decision rule and selective d-dimer use on the yield of pulmonary CT angiography (CTA).
MATERIALS AND METHODS: Guidelines incorporating a clinical decision rule (Wells score: range, 0-12.5) and a highly sensitive d-dimer assay as decision points were placed into a computerized order entry menu. From December 2006 through November 2008, 261 pulmonary CTA examinations of 238 men and 14 women (mean age ± SD, 65 ± 12 years; range, 31-92 years) were performed. Eight patients underwent more than one pulmonary CTA examination. Charts were reviewed. The results of pulmonary CTA, the clinical decision rule, and d-dimer level (if obtained) were analyzed with the Student t test, chi-square test, or other comparisons using statistical software (MedCalc, version 11.0).
RESULTS: Of the pulmonary CTA examinations, 16.5% (43/261) were positive for pulmonary embolism (PE) compared with 3.1% (6/196) during the previous 2 years. The mean clinical decision rule score and mean d-dimer level were 5.5 ± 2.4 (SD) and 4956 ± 2892 ng/mL, respectively, for those with PE compared with 4.5 ± 2.1 and 2398 ± 2100 ng/mL for those without PE (both, p < 0.01). The negative predictive value of a clinical decision rule score of 4 or less and d-dimer level of less than 1000 ng/mL was 1.0. A clinical decision rule of greater than 4 and a higher d-dimer level were better predictors for PE, especially a d-dimer level of greater than 3000 ng/mL (odds ratio = 6.69; 95% CI = 2.72-16.43).
CONCLUSION: Guidelines combining a clinical decision rule with d-dimer level significantly improved the utilization of pulmonary CTA and positive yield for PE.