title: Factor VIII assay variability in postinfusion samples containing full length and B-domain deleted FVIII.
abstract: BACKGROUND
  Although the variability in factor VIII (FVIII):C measurement is well recognized, this has not been widely reported for post-FVIII infusion samples.
  
  
  OBJECTIVE
  Three samples from haemophilia A patients were distributed in a UK National External Quality Assessment Scheme survey, each after treatment with either ReFacto AF, Kogenate FS or Advate. Fifty-two UK haemophilia centres performed FVIII assays using one-stage (n = 46) and chromogenic (n = 10) assays. Centres calibrated assays with the local plasma standard and with ReFacto AF laboratory standard for the ReFacto AF sample.
  
  
  CONCLUSIONS
  Chromogenic assays gave significantly higher results than one-stage assays (P < 0.0001, 32% difference) in the post-Kogenate sample but not in the post-ReFacto AF (11% higher by chromogenic assay, ns) or post-Advate samples (3% lower by chromogenic, ns) when assays were calibrated with plasma standards. Twenty centres used all Instrumentation Laboratory (IL)-activated partial thromboplastin time reagents (Synthasil)/IL deficient plasma/reference plasma) in the one-stage assay and 15 used all Siemens reagents (Actin FS/Siemens deficient plasma/reference plasma); this made a significant difference to results post-ReFacto AF (41% higher by IL reagents, P < 0.0001) and Advate (39% higher by IL reagents, P < 0.0001), but not Kogenate (7% higher by IL, ns) when calibrated with plasma standards. Differences between results obtained with different one-stage assay reagents for monitoring Advate have implications for dosing patients. Furthermore, there was considerable inter-laboratory variation as indicated by CVs in the range 15-26% for chromogenic assay and 12-19% for one-stage assay results. This study suggests that external quality assessment schemes should offer participation in post-FVIII infusion schemes where haemophilic patients are monitored.
authors.affiliation: UK NEQAS Blood Coagulation, Sheffield, UK. steve.kitchen@sth.nhs.uk.|Sheffield Haemophilia and Thrombosis Centre, Sheffield, UK. steve.kitchen@sth.nhs.uk.
authors.forename: S
authors.initials: S
authors.lastname: Kitchen
authors.affiliation: UK NEQAS Blood Coagulation, Sheffield, UK.
authors.forename: I
authors.initials: I
authors.lastname: Jennings
authors.affiliation: UK NEQAS Blood Coagulation, Sheffield, UK.|Department of Cardiovascular Science, University of Sheffield, Sheffield, UK.
authors.forename: M
authors.initials: M
authors.lastname: Makris
authors.affiliation: UK NEQAS Blood Coagulation, Sheffield, UK.
authors.forename: D P
authors.initials: DP
authors.lastname: Kitchen
authors.affiliation: UK NEQAS Blood Coagulation, Sheffield, UK.
authors.forename: T A L
authors.initials: TA
authors.lastname: Woods
authors.affiliation: UK NEQAS Blood Coagulation, Sheffield, UK.
authors.forename: I D
authors.initials: ID
authors.lastname: Walker
mesh_terms: D001780:Blood Coagulation Tests / Q000592:standards; D002863:Chromogenic Compounds / Q000737:chemistry; D003029:Coagulants / Q000032:analysis* / Q000592:standards / Q000627:therapeutic use; D005169:Factor VIII / Q000032:analysis* / Q000592:standards / Q000627:therapeutic use; D006467:Hemophilia A / Q000188:drug therapy; D006801:Humans; D010314:Partial Thromboplastin Time; D011933:Reagent Kits, Diagnostic
chemical_list: D002863:Chromogenic Compounds; D003029:Coagulants; D011933:Reagent Kits, Diagnostic; C078147:F8 protein, human; D005169:Factor VIII
keywords: BDD FVIII; chromogenic FVIII assay; full-length recombinant FVIII; monitoring FVIII; one-stage FVIII assay