Background Increasing the threshold to define a positive D-dimer could reduce unnecessary computed tomographic pulmonary angiography (CTPA) for suspected PE but might increase rates of missed PE and missed pneumonia, the most common nonthromboembolic diagnosis seen on CTPA. Objective Measure the effect of doubling the standard D-dimer threshold for “PE unlikely” Revised Geneva (RGS) or Wells’ scores on the exclusion rate, frequency and size of missed PE and missed pneumonia. Methods Patients evaluated for suspected PE with 64-channel CTPA were prospectively enrolled from EDs and inpatient units of four hospitals. Pretest probability data were collected in real time and the D-dimer was measured in a central laboratory. Criterion standard was CPTA interpretation by two independent radiologists combined with clinical outcome at 30 days. Results Of 678 patients enrolled, 126 (19%) were PE+ and 93 (14%) had pneumonia. Use of either Wells≤4 or RGS≤6 produced similar results. For example, with RGS≤6 and standard threshold (<500 ng/mL), D-dimer was negative in 110/678 (16%), and 4/110 were PE+ (posterior probability 3.8%), and 9/110 (8.2%) had pneumonia. With RGS≤6 and a threshold <1000 ng/mL, D-dimer was negative in 208/678 (31%) and 11/208 (5.3%) were PE+, but 10/11 missed PEs were subsegmental, and none had concomitant DVT. Pneumonia was found in 12/208 (5.4%) with RGS≤6 and D-dimer<1000 ng/mL. Conclusions Doubling the threshold for a positive D-dimer with a PE unlikely pretest probability could reduce CTPA scanning with a slightly increased risk of missed isolated subsegmental PE, and no increase in rate of missed pneumonia.

Background-Use of pretest probability can reduce unnecessary testing. We hypothesize that quantitative pretest probability, linked to evidence-based management strategies, can reduce unnecessary radiation exposure and cost in low-risk patients with symptoms suggestive of acute coronary syndrome and pulmonary embolism. Methods and Results-This was a prospective, 4-center, randomized controlled trial of decision support effectiveness.Subjects were adults with chest pain and dyspnea, nondiagnostic ECGs, and no obvious diagnosis. The clinician provided data needed to compute pretest probabilities from a Web-based system. Clinicians randomized to the intervention group received the pretest probability estimates for both acute coronary syndrome and pulmonary embolism and suggested clinical actions designed to lower radiation exposure and cost. The control group received nothing. Patients were followed for 90 days. The primary outcome and sample size of 550 was predicated on a significant reduction in the proportion of healthy patients exposed to >5 mSv chest radiation. A total of 550 patients were randomized, and 541 had complete data. The proportion with >5 mSv to the chest and no significant cardiopulmonary diagnosis within 90 days was reduced from 33% to 25% (P=0.038). The intervention group had significantly lower median chest radiation exposure (0.06 versus 0.34 mSv; P=0.037, Mann-Whitney U test) and lower median costs ($934 versus $1275; P=0.018) for medical care. Adverse events occurred in 16% of controls and 11% in the intervention group (P=0.06). Conclusions-Provision of pretest probability and prescriptive advice reduced radiation exposure and cost of care in lowrisk ambulatory patients with symptoms of acute coronary syndrome and pulmonary embolism. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01059500.(Circ Cardiovasc Imaging. 2014;7:66-73.)