title: Risk of venous thromboembolism in patients with borderline quantitative D-dimer levels.
abstract: OBJECTIVE
  The lower threshold for D-dimer in evaluating patients with low clinical risk of venous thromboembolism (VTE) ranges from 200 to 500 ng/mL. We compared the rates of VTE in patients based on D-dimer values. We hypothesized that the rate of VTE in low-risk patients with D-dimer levels less than 500 would be less than 1%.
  
  
  METHODS
  
  
  
  METHODS
  This was a retrospective chart review:
  
  
  METHODS
  The study was performed in a academic, suburban emergency department (ED).
  
  
  METHODS
  Emergency department patients with suspected VTE and D-dimer obtained were included in the study. D-dimer assay: The D-dimer assay is a quantitative instrumentation latex suspension of plasma specimens.
  
  
  RESULTS
  Presence of VTE within 30 days of ED visit.
  
  
  METHODS
  Assuming a 0% event rate in patients with D-dimer levels between 200 and 500 ng/mL, a sample of 450 patients would result in a 95% confidence interval upper limit of 0.6%.
  
  
  RESULTS
  There were 1270 ED patients with suspected VTE in which D-dimer levels were performed between October 2005 and October 2006. Patient mean age was 47.8 +/- 19.3 years; 63.2% were female, 78.2% were white. Of all D-dimer levels, 497 (39.1%) were less than 200 ng/mL, 479 (37.7%) were between 200 and 500 microg/mL, and 294 (23.1%) were greater than 500 ng/mL. There were no VTE events diagnosed in any of the patients with D-dimer levels less than 200 ng/mL. Four patients with D-dimer levels between 200 and 500 microg/mL had a pulmonary embolism on computed tomography angiography. Of these 4 patients, 3 had moderate clinical risk based on Well's criteria and one had a false-positive computed tomography. There were no cases of VTE in the remaining 475 patients (0%; 95% confidence interval 0%-0.6%).
  
  
  CONCLUSIONS
  The rate of confirmed VTE in low-risk patients with D-dimer levels between 200 and 500 ng/mL is very low. Low-risk patients with suspected VTE with D-dimer levels less than 500 ng/mL might not require additional testing.
authors.affiliation: Bellevue/NYU Medical Center New York, NY 10016, USA.
authors.forename: Taku
authors.initials: T
authors.lastname: Taira
authors.forename: Breena R
authors.initials: BR
authors.lastname: Taira
authors.forename: Matt
authors.initials: M
authors.lastname: Carmen
authors.forename: Jasmine
authors.initials: J
authors.lastname: Chohan
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Singer
mesh_terms: D004636:Emergency Service, Hospital; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011655:Pulmonary Embolism / Q000097:blood / Q000175:diagnosis; D012189:Retrospective Studies; D012307:Risk Factors; D012680:Sensitivity and Specificity; D054556:Venous Thromboembolism / Q000097:blood / Q000175:diagnosis*
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D