Factor VIII assay variability in postinfusion samples containing full length and B‐domain deleted FVIII. (24th May 2016) - Kitchen, S.
Abstract : Introduction: Although the variability in factor VIII (FVIII):C measurement is well recognized, this has not been widely reported for post‐FVIII infusion samples. Aim/Methods: 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. Results/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.