Evaluation of three automated chromogenic FVIII kits for the diagnosis of mild discrepant haemophilia A

Summary In some mild haemophilia A patients (discrepant phenotype), coagulation FVIII levels by one‐stage assay (FVIII‐1st) are more than double those by classical two‐stage coagulation assay (FVIII‐2st), and may fall within the normal range. Our aim was to assess automated two‐stage chromogenic FVIII assays (FVIII‐chr) for diagnosis of mild discrepant haemophilia A. Three chromogenic FVIII kits (Biophen, Coamatic and Dade‐Behring) were evaluated, using recommended and extended incubation times. Samples were tested from patients with discrepant haemophilia (n = 7) and equivalent mild haemophilia (agreement between FVIII‐1st and FVIII‐2st, n = 4). For equivalent haemophilia, FVIII‐chr were consistent with FVIII‐1st and FVIII‐2st for all kits at all incubation times. For discrepant haemophilia, using recommended incubation times, mean FVIII‐chr using Biophen reagents was 22 IU/dl (range 13–31), with Coamatic 26 (17–34) and with Dade‐Behring 41 (33–47), compared with 36 (27–44) for FVIII‐1st and 8 (6–9) for FVIII‐2st. FVIII‐chr decreased as incubation time was increased with Biophen and Coamatic, but decreased less with Dade‐Behring. FVIII‐chr using the Dade‐Behring kit gave similar results to FVIII‐1st and is not suitable for diagnosis of mild discrepant haemophilia A. FVIII‐chr by Biophen and Coamatic kits is suitable for diagnosis of these patients, especially with an extended incubation time.