In vitro kinetics of factor VIII activity in patients with mild haemophilia A and a discrepancy between one-stage and two-stage factor VIII assay results.
In some mild haemophilia A patients (discrepant haemophilia), factor VIII coagulant activity (FVIII:C) levels, by one-stage assay are more than double than those by two-stage assay. This may be due to the longer incubation times (10-12 min) in the two-stage assay. This study aimed to determine the time course of the activation phase of the two-stage assay, using both classical coagulation and chromogenic detection methods. In both systems, for equivalent patients (equivalent FVIII:C levels by one-stage and two-stage assays, n = 6, all different mutations), similar FVIII:C results were obtained with short- or long-incubation times. In contrast, plasma from discrepant patients (n = 8, five different mutations) showed higher FVIII:C at shorter incubation times than after longer incubation times. In the chromogenic assay, FVIII:C levels were higher after incubation for 2 min (23-56%, mean 41%) than after 10 min (19-41%, mean 29%). In the classical coagulation assay, FVIII:C levels were higher at shorter incubation times (21-64%, mean 37%) than with the longer incubation times usually used (13-29%, mean 23%). These time-course experiments have verified that the longer incubation time used in the two-stage assay is at least partly responsible for the lower FVIII:C measured by that assay in discrepant haemophilia.
Rodgers
Susan E
SE
Haematology Division, Institute of Medical and Veterinary Science, University of South Australia, Adelaide, Australia. susan.rodgers@imvs.sa.gov.au
Duncan
Elizabeth M
EM
Barbulescu
Denise M
DM
Quinn
Diana M
DM
Lloyd
John V
JV
D001780:Blood Coagulation Tests; D002863:Chromogenic Compounds / Q000494:pharmacology; D005169:Factor VIII / Q000235:genetics / Q000493:pharmacokinetics*; D006467:Hemophilia A / Q000097:blood* / Q000235:genetics*; D006801:Humans; D009154:Mutation; D011237:Predictive Value of Tests; D013925:Thromboplastin / Q000378:metabolism; D013997:Time Factors
D002863:Chromogenic Compounds; D005169:Factor VIII; D013925:Thromboplastin