Fig. 4.

The time to initiate enzyme activity (initation times) for a single plasma containing controlled levels of specific coagulation factors. Immunodepleted human plasma was reconstituted at indicated coagulation factor levels and incubated with the chromogenic substrate S-2366 and thromboplastin-coated microspheres at a count of 10⁴ mL⁻¹ for 3 minutes at 37°C prior to recalcification (8.3 mM, final Ca²⁺ concentration). Absorbance of light (405 nm) was recorded with a spectrometer at 1 minute intervals. Samples yielded a sigmoid relationship between absorbance and time, and the initiation time was recorded as the time when absorbance increased above baseline. Experiments were performed in duplicate, with the mean clotting time reported. The data points represent the mean initiation time (n=3) and the error bars represent standard error. The gray regions represent the reported range of normal coagulation factor levels.