Assessment of the bleeding phenotype in FIX^nullrecipients that received 2bCoF9R338L-transduced HSCs (the noninhibitor model). At least 6 months after transplantation, the bleeding phenotype was assessed by a 6-hour tail bleeding test and a needle-induced knee joint injury model. The functional hemostatic properties in whole blood were assessed by ROTEM and nWB-TGA analysis. For the tail bleeding test, the tail tip was clipped using a 1.6-mm diameter template. Animals were monitored hourly, and bleeding time was recorded. Fifty-microliter blood samples were collected for blood counts before and after the test. Hemoglobin levels before the test were defined as 100%. For the knee joint injury, a G30 × 1/2 needle was used to induce injury in the right knee, leaving the left knee uninjured as an intra-animal control. The diameter of the knee joint was measured by using a digital micro caliper before and 48 hours after injury. The diameter of the knee joint before the injury was defined as 1. For ROTEM and TGA analysis, blood samples were drawn from the vena cava. WT C57BL/6 and FIX^null mice served as controls. (A) Bleeding time from the tail bleeding test. (B) Percentage of hemoglobin remaining after the tail bleeding test. (C) The ratio of knee joint diameter obtained from 48 hours after compared with before the injury. (D) ROTEM analysis of whole blood. (E) TGA analysis of whole blood. Data are presented as mean ± SD except for panel B, which are presented in a box and whisker plot. *P < .05; **P < .01; ***P < .001; ****P < .0001.