Observations on Factor X Activity after Adsorption to Barium Sulphate

Summary The amount of preformed clotting activity exhibited by factor X was found to be closely related to the bulk density of the barium sulphate used for its adsorption from serum. The X-ray grade of barium sulphate compares closely with that manufactured by precipitation and its bulk density is half that of the soil grade which is similar to the material obtained by grinding natural barytes. Microscopically, the soil grade shows an irregular crystalline surface and when used for the adsorption of serum, the resulting eluate has a greater clotting and esterase activity than is the case when the X-ray grade, which has a smooth surface, is used. Possible mechanisms leading to the surface activation of factor X by barium sulphate are discussed and the findings are also related to earlier observations on variations in the availability of serum thrombotic accelerator (STA) after its adsorption to the same grade of barium sulphate. The importance of defining the barium sulphate used for the adsorption of clotting factors in terms of its physical properties and microscopic appearance is emphasised.