In EU: This Product is CE Marked. Deficient plasma for the assay of Factor XII. All the clotting factors are present (constant and in the normal range, brought by the deficient plasma), except for FXII, which is brought by the diluted tested plasma, and clotting is triggered with cephalin, activator and calcium (APTT). FXII is the limiting factor and clotting time is inversely proportional to the concentration of FXII.