In vitro thrombogenicity tests of factor IX concentrates. II: effects of phospholipids and heparin.

Measurement of the total phospholipid (and that portion active in coagulation) in factor IX concentrates revealed no correlation with in vitro tests of potential thrombogenicity, except in the case of the recalcification time and the thrombin generation test which may detect coagulant phospholipid as well as the presence of thrombogenic enzymes. This is probably due to separation of the prothrombin complex proteins from most phospholipid during ion-exchange chromatography. Although low levels of phospholipid remain in the final product these are apparently insufficient to effect appreciable activation of factor IX concentrates despite low levels of antithrombin III. Two tests which measure the formation of thrombin and factor Xa after recalcification of concentrates were affected by the addition of exogenous phospholipid. However this is a relative effect such that differences are quantitative rather than qualitative. Heparin addition during production of factor IX concentrate was found to have only minor effects on the results of in vitro thrombogenicity tests of the final product. This was confirmed in the laboratory by incubation of unheparinised products with heparin for periods of up to 6 hr.