title: Testing for hereditary thrombophilia: a retrospective analysis of testing referred to a national laboratory.
abstract: BACKGROUND
  Predisposition to venous thrombosis may be assessed through testing for defects and/or deficiencies of a number of hereditary factors. There is potential for confusion about which of these tests are appropriate in which settings. At least one set of recommendations has been published to guide such testing, but it is unclear how widely these have been disseminated.
  
  
  METHODS
  We performed a retrospective analysis of laboratory orders and results at a national referral laboratory to gain insight into physicians' ordering practices, specifically comparing them against the ordering practices recommended by a 2002 College of American Pathologists (CAP) consensus conference on thrombophilia testing. Measurements included absolute and relative ordering volumes and positivity rates from approximately 200,000 thrombophilia tests performed from September 2005 through August 2006 at a national reference laboratory. Quality control data were used to estimate the proportion of samples that may have been affected by anticoagulant therapy. A sample of ordering laboratories was surveyed in order to assess potential measurement bias.
  
  
  RESULTS
  Total antigen assays for protein C, protein S and antithrombin were ordered almost as frequently as functional assays for these analytes. The DNA test for factor V Leiden was ordered much more often than the corresponding functional assay. In addition, relative positivity rates coupled with elevations in prothrombin time (PT) in many of these patients suggest that these tests are often ordered in the setting of oral anticoagulant therapy.
  
  
  CONCLUSIONS
  In this real-world setting, testing for inherited thrombophilia is frequently at odds with the recommendations of the CAP consensus conference. There is a need for wider dissemination of concise thrombophilia testing guidelines.
authors.affiliation: University of Utah Department of Pathology, Salt Lake City, UT, USA. brian.jackson@aruplab.com
authors.forename: Brian R
authors.initials: BR
authors.lastname: Jackson
authors.forename: Kyland
authors.initials: K
authors.lastname: Holmes
authors.forename: Amit
authors.initials: A
authors.lastname: Phansalkar
authors.forename: George M
authors.initials: GM
authors.lastname: Rodgers