Clotting times of commercial FIX deficient plasmas measured by a partial thromboplastin time assay. Partial thromboplastin time (aPTT) assay to determine clotting time of FIX-deficient commercial plasma (A: HTI plasma, B: Stago plasma) with different concentrations of FIXa in the presence and absence of PS antibody. (A) Clotting time of different samples of HTI FIX-deficient plasma. The plasma was incubated with different concentrations of FIXa, and clotting times were measured in the absence (red bar) and presence (orange bar) of PS antibody (450 nM). (B) The same experiment with Stago plasma. Light green and dark green bars represent the clotting time without and with PS antibody, respectively. (A1,B1) The bottom panels in panels A and B show data presented in each panel in a single scatterplot of log(0.001 + dose) vs clotting time for all samples. The dashed lines represent the fitting by the log-linear model. The y-axis scales vary between graphs for greater visibility of results.