Assay of Fletcher factor (plasma prekallikrein) using an artificial clotting reagent and a modified chromogenic assay

An artificial clotting reagent lacking in Fletcher factor (plasma prekallikrein, PPK) was made by mixing human plasma, activated by 5 mg/ml of celite, then kept 16 hours at 37 degrees to destroy most of the plasma kallikrein, plus rabbit plasma (which is devoid of XII and Fletcher activity). Chromogenic assay using a tripeptide substrate was also modified to exclude the interference of the endogenous contact factors. Celite eluate was used instead of kaolin or dextran sulphate for the activation. Using both these methods, it is possible to distinguish between Fletcher trait (PPK deficiency) and other contact factors such as factor XII and HMWK deficiencies, which do not activate with kaolin or dextran sulphate. These simple clotting and enzymatic assays give specific and well correlated results for PPK estimation.