In US: For Research Use Only. Not for Use in Diagnostic Procedures. Chromogenic assay for the measurement of Factor VIII:C activity in human citrated plasma, Factor VIII:C concentrates, or biological fluids. Automated or Manual method. Calibrator plasma and controls (at two levels) are available. This assay offers two working ranges for Factor VIII:C (Low: 0 to 25% and High: 0 to 200%).