Application of a Novel and Rapid Whole Blood Assay for D-Dimer in Patients with Clinically Suspected Pulmonary Embolism

STUDY OBJECTIVE: To determine the clinical utility of a novel whole blood assay for D-dimer (SimpliRED) in patients with clinically suspected pulmonary embolism (PE). DESIGN: Prospective cohort. PATIENTS: Eighty-six consecutive patients with clinically suspected PE. INTERVENTION: All patients had the SimpliRED D-dimer assay performed and underwent ventilation/perfusion (V/Q) lung scanning and bilateral impedance plethysmography (IPG); pulmonary angiography was performed in two patients. Patients were classified as: 1) PE-positive; positive pulmonary angiography or high probability V/Q scan or non-high probability V/Q scan and either abnormal IPG (either at presentation or upon serial testing and confirmed by contrast venography) or symptomatic thromboembolic event within three months of presentation or 2) PE-negative; normal V/Q scan or normal pulmonary angiography or non-high probability V/Q scan and normal serial IPG and absence of symptomatic venous thromboembolism within three months of follow up. Sixteen (19%) patients were classified as PE-positive and 70 (81%) patients were classified as PE-negative. MEASUREMENTS AND RESULT: The sensitivities, specificities, positive predictive values, and negative predictive values of the D-dimer assay were calculated for all patients and for the subgroup of patients without comorbid conditions that independently can cause elevated D-dimer levels. The D-dimer showed a sensitivity of 94%, a negative predictive value of 98%, a specificity of 66%, and a positive predictive value of 38%. In the subgroup of patients without comorbid conditions, the specificity increased to 98% and the positive predictive value to 83%, but because only six patients had an abnormal D-dimer level, the 95% confidence interval on the observed positive predictive value is wide (36-100%). CONCLUSIONS: This study demonstrates that the SimpliRED D-dimer assay, which can be performed and interpreted at the bedside within five minutes, has potential clinical utility as an exclusionary test in patients with clinically suspected PE. The assay should be evaluated in large clinical management studies.