title: D-dimer: simple test, tough problems.
abstract: BACKGROUND
  D-dimer is widely used for exclusion, or as an aid in diagnosis, of venous thromboembolism (VTE); however, the D-dimer assay methods available from manufacturers and the laboratory application of those methods vary widely.
  
  
  OBJECTIVE
  To describe the current laboratory practice regarding the assay and reporting of D-dimer.
  
  
  METHODS
  Laboratories' D-dimer proficiency testing data were analyzed and laboratory practices regarding the performance and reporting of D-dimer were surveyed.
  
  
  RESULTS
  Initial grading of D-dimer proficiency testing demonstrated high variability within and among methods. This variability continued to be present for several years after attempts to intervene. The number of laboratories using D-dimer to exclude VTE grew from 1500 in 2004 to more than 3500 in 2012. Survey and proficiency testing data demonstrated that 33% of laboratories changed the type or magnitude of units from that recommended by the manufacturer, a practice associated with as much as a 20-fold increase in the failure of proficiency testing. Many laboratories used a threshold for the exclusion of VTE that is higher than that recommended by the manufacturer. Many laboratories continue to use qualitative assays with insufficient sensitivity for exclusion of VTE.
  
  
  CONCLUSIONS
  There is considerable variability both within and among quantitative methods used to assay D-dimer by laboratories. Laboratory practice continues to vary widely regarding the type and magnitude of units reported and the setting of the threshold for the exclusion of VTE. Although improved, the variability continues despite initial efforts to intervene.
authors.affiliation: Department of Pathology, University of Texas Health Science Center, San Antonio, TX 78229-3900, USA. olsonj@uthscsa.edu
authors.forename: John D
authors.initials: JD
authors.lastname: Olson
authors.forename: Mark T
authors.initials: MT
authors.lastname: Cunningham
authors.forename: Russell A
authors.initials: RA
authors.lastname: Higgins
authors.forename: Charles S
authors.initials: CS
authors.lastname: Eby
authors.forename: John T
authors.initials: JT
authors.lastname: Brandt
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D003625:Data Collection; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D006801:Humans; D059021:Laboratory Proficiency Testing; D015203:Reproducibility of Results; D054556:Venous Thromboembolism / Q000097:blood* / Q000175:diagnosis*
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D