6.0 and high if the score was over 6.0. Pulmonary embolism unlikely was assigned to patients with scores 4.0 and PE likely if the score was >4.0. 7.8% of patients with scores of less than or equal to 4 had PE but if the D-dimer was negative in these patients the rate of PE was only 2.2% (95% CI = 1.0% to 4.0%) in the derivation set and 1.7% in the validation set. Importantly this combination occurred in 46% of our study patients. A score of <2.0 and a negative D-dimer results in a PE rate of 1.5% (95% CI = 0.4% to 3.7%) in the derivation set and 2.7% (95% CI = 0.3% to 9.0%) in the validation set and only occurred in 29% of patients. The combination of a score 4.0 by our simple clinical prediction rule and a negative SimpliRED D-Dimer result may safely exclude PE in a large proportion of patients with suspected PE. Introduction Pulmonary embolism, the third leading cause of cardiovascular mortality in North America, has an estimated annual incidence of 23 cases per 100,000 population per year (1). Since PE is present in less then 35% of investigated patients unnecessary presumptive anti- coagulation, admission to hospital and testing occurs in a large number of patients without PE (2). A bedside method that safely excludes PE would be desirable. Since untreated PE has a high hospital mortality rate, which falls with appropriate treatment (3), a bedside method needs to be highly sensitive (i.e. very few false negatives). In addition, for a bedside test to be clinically useful it must exclude a large proportion of patients who do not have the disease. Until recently the clinical diagno- sis of PE was also felt to be inaccurate and of little value. The PIOPED investigators revisited the accuracy of the clinical diagnosis and demonstrated that experienced clinicians were able to separate cohorts of patients with suspected PE into high, moderate and low probability groups using the clinical assessment alone in a multicentre study in which the diagnosis of PE was confirmed by pulmonary angiography (2). Realizing the potential utility of identifying pretest probability we recently developed an explicit clinical model to determine likelihood for PE using clinical findings, ECG and chest x-ray results (4). The clinical model was rather complex (Fig. 1). It consisted of conside- ration of whether the patients clinical presentation based on symptoms, signs and risk factors, was typical for PE and whether there was an alternative diagnosis at least as likely as PE to account for their symptoms. Evaluating over 1200 inpatients and outpatients with suspected PE we were able to distinguish low, moderate, and high probability cohorts in whom the incidence rates of PE were 3%, 28% and 78%, respectively (4). Consideration of clinical probability was a 416 Thromb Haemost 2000; 83: 416 – 20 © 2000 Schattauer Verlag, Stuttgart Derivation of a Simple Clinical Model to Categorize Patients Probability of Pulmonary Embolism: Increasing the Models Utility with the SimpliRED D-dimer Philip S. Wells, David R. Anderson, Marc Rodger, Jeffrey S. Ginsberg, Clive Kearon, Michael Gent, Alexander G. G. Turpie, Janis Bormanis, Jeffrey Weitz, Michael Chamberlain, Dennis Bowie, David Barnes, Jack Hirsh From the Departments of Medicine, University of Ottawa, Ottawa, Canada, McMaster University, Hamilton, Canada, Dalhousie University, Halifax, Canada Key words Pulmonary embolism, diagnosis, D-dimer, clinical assessment, regression analysis Summary We have previously demonstrated that a clinical model can be safely used in a management strategy in patients with suspected pulmo- nary embolism (PE). We sought to simplify the clinical model and determine a scoring system, that when combined with D-dimer results, would safely exclude PE without the need for other tests, in a large proportion of patients. We used a randomly selected sample of 80% of the patients that participated in a prospective cohort study of patients with suspected PE to perform a logistic regression analysis on 40 clini- cal variables to create a simple clinical prediction rule. Cut points on the new rule were determined to create two scoring systems. In the first scoring system patients were classified as having low, moderate and high probability of PE with the proportions being similar to those determined in our original study. The second system was designed to create two categories, PE likely and unlikely. The goal in the latter was that PE unlikely patients with a negative D-dimer result would have PE in less than 2% of cases. The proportion of patients with PE in each category was determined overall and according to a positive or nega- tive SimpliRED D-dimer result. After these determinations we applied the models to the remaining 20% of patients as a validation of the results. The following seven variables and assigned scores (in brackets) were included in the clinical prediction rule: Clinical symptoms of DVT (3.0), no alternative diagnosis (3.0), heart rate >100 (1.5), immo- bilization or surgery in the previous four weeks (1.5), previous DVT/PE (1.5), hemoptysis (1.0) and malignancy (1.0). Patients were considered low probability if the score was <2.0, moderate of the score was 2.0 to Funding for this study was provided by the National Health Research and Development Program of Canada (project #6606-5283-403). Dr. Philip Wells, David Anderson, Clive Kearon and Jeffrey Ginsberg are the recipients of Research Scholarships from the Heart and Stroke Foundation of Canada. Dr.Weitz is a recipient of a Career Investigator Award from the Heart and Stroke Foundation of Ontario, and Dr. Hirsh is a Distinguished professor of the Heart and Stroke Foundation of Canada. Correspondence to: Dr. Philip Wells, Suite 467, 737 Parkdale Avenue, Ottawa, Ontario, K1Y 1J8, Canada – Tel.: +613 761 4127; Fax: +613 761 4840; E-mail: pwells@civich.ottawa.on.ca For personal or educational use only. No other uses without permission. All rights reserved. Downloaded from www.thrombosis-online.com on 2015-08-12 | ID: 1000481178 | IP: 140.254.70.165