WBCT of rFIXFc versus rFIX in FIX-deficient mice. FIX-deficient mice (6 per group) were dosed intravenously with rFIXFc at 50 IU/kg body weight or rFIX at 50 IU/kg body weight. Blood samples were collected before dosing and at various times after dosing. Blood samples were incubated at 37°C and were visually inspected for the presence of a blood clot once per minute. The time needed for a clot to form was recorded, and, once the clotting activity returned to baseline (ie, no clot formation), no additional samples were obtained (samples collected 15 minutes to 144 hours for rFIXFc or 15 minutes to 72 hours for rFIX). The graph indicates the percentage of animals able to clot blood at each time point.