title: D-dimer assays--a help or hindrance in suspected pulmonary thromboembolism assessment?
abstract: BACKGROUND
  Suspected pulmonary thromboembolism (PTE) is a common presentation to acute medical units and can cause diagnostic difficulty. National guidelines on PTE management highlight the need for clinical probability assessment and D-dimer assays to ensure appropriate use of diagnostic imaging. D-dimers are used widely in UK hospitals, yet concern exists regarding their misuse.
  
  
  OBJECTIVE
  In this study we aimed to assess the impact of the introduction of D-dimer assays, combined with clinical probability assessment, for evaluation of suspected PTE in our unit.
  
  
  METHODS
  This was a prospective audit of all patients presenting with suspected PTE over two 12-week periods, exactly 1 year apart. D-dimers were introduced into our unit between these two periods. We recorded the clinical probability score, potential causes of false-positive D-dimer assay, diagnostic imaging result, patient outcome, admission rates, and length of inpatient stay.
  
  
  METHODS
  Categorical variables were compared using a 2 x 2 chi-square test or Fisher's exact test. Groups were compared utilizing the two-sample t-test or Mann-Whitney U test.
  
  
  RESULTS
  A total of 190 patients were included in the study; 65% were female. PTE was confirmed in 8.4%. Patients in both audit periods were comparable with regard to suitability for D-dimer measurement. Following D-dimer introduction, 40 out of 110 patients in period 2 could be discharged directly from the emergency department. Of those admitted to hospital, the median length of stay was significantly reduced in period 2 (3 days in period 1 vs 1 day in period 2; P=0.0007). Use of diagnostic imaging was significantly reduced following the introduction of D-dimers (90% in period 1 vs 40% in period 2; P<0.0001). The positive diagnostic yield for PTE on CT pulmonary angiogram (CTPA) increased significantly from 10% in period 1 to 23% in period 2 (P=0.039).
  
  
  CONCLUSIONS
  D-dimers must be used judiciously in the assessment of suspected PTE. Appropriate use of D-dimers can provide many benefits, including reductions in diagnostic imaging (and thus radiation exposure), admission rates, and length of inpatient stay.
authors.affiliation: Department of Respiratory Medicine, Southern General Hospital, Glasgow, United Kingdom. hannah.bayes@talk21.com
authors.forename: H K
authors.initials: HK
authors.lastname: Bayes
authors.forename: C A
authors.initials: CA
authors.lastname: O'Dowd
authors.forename: N J
authors.initials: NJ
authors.lastname: Glassford
authors.forename: A
authors.initials: A
authors.lastname: McKay
authors.forename: S
authors.initials: S
authors.lastname: Davidson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D003952:Diagnostic Imaging / Q000706:statistics & numerical data; D005189:False Positive Reactions; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D010343:Patient Admission / Q000706:statistics & numerical data; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000175:diagnosis*
chemical_list: D015415:Biomarkers; D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D