title: Thrombin generation assay using factor IXa as a trigger to quantify accurately factor VIII levels in haemophilia A.
abstract: BACKGROUND
  The available methods for measuring factor VIII (FVIII) activity suffer reportedly from lack of sensitivity and precision in the < 1 IU dL(-1) range. This precludes correlation of clinical phenotype with FVIII levels.
  
  
  OBJECTIVE
  To study a possible association between clinical phenotype in patients with FVIII levels < 1 IU dL(-1).
  
  
  RESULTS
  The FIXa-driven FVIII assay (FVIII-CAT) has a detection limit of 0.05 IU dL(-1). For the range of 0-2 IU dL(-1) FVIII, the intra-assay coefficient of variation (CV) is around 2% and the inter-assay CV is about 8%. We tested 30 hemophiliacs with FVIII:C between < 1 and 6 IU dL(-1) as measured in the one-stage clotting assay using the FVIII-CAT assay. For genetic defects related to moderate hemophilia, the FVIII-CAT test finds FVIII levels that are in good agreement with those determined with the one-stage assay. Of the 21 hemophilic patients with FVIII < 1 IU dL(-1), four patients exhibited a mild bleeding phenotype. When we applied TF-initiated thrombin generation, patients with a mild clinical phenotype showed significantly higher endogenous thrombin potentials.
  
  
  CONCLUSIONS
  The novel developed FVIII assay measures accurately FVIII levels below 1 IU dL(-1). Its application demonstrated that the clinical heterogeneity in individuals with < 1 IU dL(-1) FVIII is not associated with their FVIII level.
authors: Synapse BV, Maastricht, The Netherlands.
authors: M
authors: M
authors: Ninivaggi
authors: Y
authors: Y
authors: Dargaud
authors: R
authors: R
authors: van Oerle
authors: B
authors: B
authors: de Laat
authors: H C
authors: HC
authors: Hemker
authors: T
authors: T
authors: Lindhout