MEASUREMENT OF ACTIVATED FACTOR-IX IN FACTOR-IX CONCENTRATES - CORRELATION WITH IN-VIVO THROMBOGENICITY

Current in vitro tests for thrombogenicity of FIX concentrates used fo r prothrombin complex concentrates (PCCs), are of little value when ap plied to high purity FIX (HP FIXs). In the present study, we have deve loped a chromogenic assay far activated FIX (FIXa) and evaluated its a bility to predict in vivo thrombogenic potential of HP FIXs in a modif ied Wessler stasis model. Among the HP FIXs, only 1 out of 7 products had no detectable FIXa; this product also showed no in vivo thrombogen icity. In the other 6 products, FIXa content ranged from 0.15-1.2 U/10 00 iu FIX, and all showed some evidence of in vivo thrombogenicity, wi th mean thrombus scores ranging from 0.25-4. There was a significant p ositive correlation (r = 0.55, p < 0.02) between FIXa levels and in vi va thrombogenicity of HP FIXs. NAPTT data were not significantly corre lated with the in vivo results and the TFCT also showed no direct corr elation with the mean thrombus score. These results indicate that HP F IXs may still carry a small residual thrombotic risk and measurement o f FIXa content of these products may be a better predictor of thrombog enicity than the current in vitro tests.