Objective: To evaluate what specific combination of
clinical criteria and d-dimer values may yield at least a 10% positive
pulmonary embolism (PE) rate in patients undergoing pulmonary CT angiography
(CTA). Materials and Methods:Retrospective
review of all patients presenting to the Emergency Department with possible PE who
underwent pulmonary CTA and had a d-dimer drawn. Wells scores were
retrospectively assigned based on data gathered through medical records. Results: During a 29-month period, 1110 patients underwent pulmonary
CTA. Of these, 773 also had a d-dimer drawn. These subjects were stratified
based on serum d-dimer levels into negative (≤4μg/ml), nonpositive
(0.41-1.0μg/ml), or positive (>1.0μg/ml) d-dimer
categories. The prevalence of positive CTA studies was >10% only in the
positive d-dimer group. Subjects were also stratified based on their Wells
score into three clinical categories: low (score <2), intermediate
(score=2-6), and high risk of pulmonary embolism (score >6). The
prevalence of positive CTA was >10% only in the group of subjects with high
clinical risk. When stratified according to both Wells criteria and d-dimer,
only those patients with intermediate or high clinical risk combined with a
positive d-dimer (>1.0μg/ml) had a prevalence of positive pulmonary
CTA >10%. By limiting the use of CTA studies to those patients with
positive d-dimer values or high clinical risk, 438 (55.4%) patients could have
avoided CTA imaging.Conclusion: Utilizing CTA only in patients suspected
of PE with a combination of high clinical risk based on a Wells criteria
threshold score >6 and a serum d-dimer cutoff of 1μg/ml
would increase the prevalence of positive pulmonary CTA studies above 10% and
avoid a large number of CTA imaging studies.
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