Preparation of 'contact product' as a reagent for coagulation tests.

If Celite 512 is incubated with normal plasma, an activity can then be eluted from it which corresponds to the activation of contact clotting factors XII and XI. The phenomenon was described by Waaler (1959) who called the eluate 'activation product'. The material has been in routine use in this labora- tory for a number of years in the one-stage assay of factor VIII (Essien and Ingram, 1967; Hills, Ingram, and Matchett, 1970); it is also used in a screening test for defects of the 'contact' factors. The prep- aration of the reagent was described by Wilson, Ingram, and Hills (1971), but the technique has required further study because some batches have clotted during preparation, and excessive thrombin activity has sometimes remained in the final product. Different methods of defibrinating the starting plasma have therefore been investigated, and the effect of a final adsorption with alumina has been examined.