title: The investigation of a prolonged APTT with specific clotting factor assays is unnecessary if an APTT with Actin FS is normal.
abstract: BACKGROUND
  An isolated prolongation to the activated partial thromboplastin time (APTT) can be caused by the presence of the lupus anticoagulant or an intrinsic or contact factor deficiency, of which only deficiencies of factors VIII, IX or XI are associated with bleeding. Our local protocol states that further investigation of a prolonged APTT by specific assays of FVIII, FIX and FXI should only be undertaken where the APTT with one reagent (Synthasil) is more than 3 s prolonged, and further investigation by an APTT with a second reagent (Actin FS) is also prolonged, unless there is a history of bleeding in the patient, in which case assays are indicated irrespective of the APTT.
  
  
  METHODS
  We retrospectively reviewed the results of all APTTs performed over a 36-month period to evaluate whether strictly applying our protocol would reduce the number of unnecessary clotting factor assays performed, without leaving patients with potentially significant bleeding disorders undiagnosed.
  
  
  RESULTS
  Of a total number of 587 samples tested for coagulation factors VIII, IX and XI, only 117 samples yielded an abnormal result. Thus, 80% of all the assays requested in the 3-year period audited gave a result within the reference range for factors VIII, FIX and XI. Three quarters of the abnormal results revealed mild FXI deficiency.
  
  
  CONCLUSIONS
  This review has demonstrated that no significant coagulation factor deficiency would be left undiagnosed if the protocol was followed. This would have considerably reduced the cost and time spent performing these assays.
authors.affiliation: Sheffield Haemophilia and Thrombosis Centre, Sheffield, UK. Annette.bowyer@sth.nhs.uk
authors.forename: A
authors.initials: A
authors.lastname: Bowyer
authors.forename: J
authors.initials: J
authors.lastname: Smith
authors.forename: A M
authors.initials: AM
authors.lastname: Woolley
authors.forename: S
authors.initials: S
authors.lastname: Kitchen
authors.forename: K K
authors.initials: KK
authors.lastname: Hampton
authors.forename: R M
authors.initials: RM
authors.lastname: Maclean
authors.forename: J J
authors.initials: JJ
authors.lastname: VAN Veen
authors.forename: M
authors.initials: M
authors.lastname: Makris
mesh_terms: D000199:Actins / Q000097:blood; D000465:Algorithms; D001778:Blood Coagulation Disorders / Q000097:blood / Q000175:diagnosis; D001779:Blood Coagulation Factors; D006801:Humans; D010314:Partial Thromboplastin Time
chemical_list: D000199:Actins; D001779:Blood Coagulation Factors