To quantify the actual amount of factor present in a factor-deficient patient sample, one can employ another test based on the PT or aPTT assays.
This assay involves mixing various dilutions of a patient sample with the specific factor-deficient reagent plasma. The results of the various "mixtures" are then plotted against a standard curve that correlates with factor activity levels. When developing the standard curve, at least 3 points must be plotted to ensure accuracy when utilizing the curve for patient factor activity assays.
Once the standard curve has been constructed and all points plotted, the approximate amount of factor contained in the patient sample can be interpreted. The patient sample must have two or more points plotted against the standard curve, which enhances accuracy and allows for the recognition of inhibitors in the patient sample. These points must fall within the acceptable range of the standard curve to be considered valid.
Two or more assayed reference plasmas that validate the standard curve should also be tested at least every 8 hours of patient testing to ensure accuracy of patient results.