E. Gray et al., MEASUREMENT OF ACTIVATED FACTOR-IX IN FACTOR-IX CONCENTRATES - CORRELATION WITH IN-VIVO THROMBOGENICITY, Thrombosis and haemostasis, 73(4), 1995, pp. 675-679
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.