In vivo recovery and half-life time of a steam-treated factor IX concentrate in hemophilia B patients

Summary Factor IX (FIX) recovery and half-life was measured in ten hemophilia B patients under standardized conditions. Each patient received a steam-treated high-purity factor IX concentrate at a dose of 19–39 U/kg body weight. FIX activity was determined using a one-stage assay, which was calibrated against the international concentrate standard (reagents from Immuno, Heidelberg). The in vivo recovery ranged from 24% to 53% (mean value 37.7%) and the half-disappearance time (HDT) from 8–30 h (mean 16.7 h). In four of the ten patients, the distribution and elimination half-lives were estimated and ranged from 0.3 h to 3.9 h (mean 1.4 h) and from 28.6 h to 39.7 h (mean 33.1 h), respectively. In six patients FIX was redetermined using a different FIX deficient plasma and a plasma standard (reagents from Merz & Dade, Munich, FRG). Recoveries and HDT based on the results obtained with this method were significantly higher (68.2% vs 39.7%; p<0.05), and longer (14.8 h vs 10.6 h; p<0.05), respectively. FIX activity was also measured by both assay systems in 100 healthy subjects (50 males, 50 females). The reagents from Immuno yielded a mean value of 0.77 U/ml, while the mean FIX activity utilizing standards and reagents from Merz & Dade was 1.11 U/ml (p<0.000001). The coefficient of correlation between the FIX activity measurements, as determined in 100 healthy subjects and 6 hemophilia B patients using the different test systems, was r=0.9 (N=159; y=0.08+1.3 * x; p<0.001). Our data suggest that recovery and HDT of factor IX concentrate strongly depend on the assay and calibration conditions and that an international FIX activity plasma standard is urgently required.