Utilization and yield of chest computed tomographic angiography associated with low positive D-dimer levels

It is unclear to what degree broadly applied D-dimer testing combined with a low threshold for imaging with even minimally positive results may be contributing to the utilization of chest computed tomographic angiography (CTA).

To determine what proportion of chest CTAs for suspected pulmonary embolism (PE) were performed in the setting of minimally elevated D-dimer levels, and to determine the prevalence of PE in those patients when stratified by clinical risk.

Retrospective chart review of all patients who had chest CTA for the evaluation of suspected PE during the years 2002-2006 in a suburban community teaching hospital emergency department.

There were 1136 eligible patient visits, of which 353 (31.1%) were found to have D-dimer levels in the low positive range (0.5-0.99 μg/mL). Of these 353 patients, 9 (2.6%; 95% confidence interval [CI] 0.9-4.2%) were diagnosed with PE. There were also 109 patients (9.6%) who had normal D-dimer levels (<0.5 μg/mL). Two of these 109 (1.8%; 95% CI 0-4.2%) were diagnosed with PE. When stratified by the Pulmonary Embolism Rule-out Criteria, 99 of 353 patients with low positive D-dimer levels (28.0%; 95% CI 23.4-32.7%), and 14 of 109 with normal D-dimer levels (12.8%; 95% CI 6.6-19.1%) were classified as low risk, none of whom had PE.

Nearly one-third of all chest CTAs were done for patients with minimally elevated D-dimer levels, and another 9.6% for patients with normal D-dimer levels with very low yield. Further research to define clinical criteria identifying patients with minimal risk of PE despite low positive D-dimer levels represents an opportunity to improve both patient safety and utilization efficiency of chest CTA.