Study of a Proposed International Standard for Blood Coagulation Factor IX

Abstract

SummaryAn International Collaborative Study was organized to establish a standard for factor IX. Two freeze-dried concentrate preparations, C1 and C2, and one freeze-dried plasma P were compared with each other, with fresh normal plasmas and with local standards in 13 laboratories. One of the concentrate preparations (C1) contained heparin and this gave rise to non-parallel assays in laboratories testing concentrate C1 in dilutions containing more than 0.05 i.u. of heparin per ml.Assays of factor IX showed good precision for both plasma and concentrate in all laboratories; no systematic effect of method, operator or day of assay was detected.The plasma preparation P and the concentrate preparation C2 were compared with 59 individual fresh normal plasma samples, and a mean potency ratio of 0.78 (95% confidence Hmits 0.73-0.84) for plasma and 5.62 (95 % confidence limits 5.13-6.16) for the concentrate C2 obtained. Only 21 estimates of concentrate C1 in terms of fresh plasma were obtained giving a mean potency ratio of 3.85 (95% confidence limits 1.87—7.92).The estimated loss of potency for freeze-dried plasma stored at — 20° C is approximately 0.4% per year. The concentrate C2 is apparently more stable and only very small losses occurred even at higher storage temperatures.All participants agreed that the preparation C2 would be suitable to serve as an International Standard for factor IX; they also agreed that the figure assigned for the unitage should be based on the number of ml of ‘average fresh normal plasma’ estimated to contain the factor IX activity of one ampoule of the preparation. It is proposed to recommend to the World Health Organization that the preparation of factor IX concentrate C2, in ampoules coded 72/32, be considered for establishment as the International Standard for factor IX, and that the international unit for factor IX be assigned on the basis of 5.62 units per ampoule of this preparation.

Recombinant factorIX: discrepancies between one‐stage clotting and chromogenic assays

“…The IS has an important role in defining the IU and harmonizes potencies of FIX products between laboratories. The first IS for FIX concentrate was established in 1976 and the continuity of the IU has been ensured by value assignment of successive IS relative to the preceding IS.…”

Standards and monitoring treatment

“…Factor IX As for FVIII, a FIX concentrate standard was the first to be established by the WHO for therapeutic materials [12]. Subsequently, an international plasma standard for FIX, together with the other vitamin K‐dependent factors II, VII and X, was established by the WHO in 1987 [13].…”

Standardization of Assays in Hemophilia

“…As for FVIII, a concentrate standard was the first to be established by WHO, for therapeutic materi als, and this consisted of a prothrombin complex concentrate (PCC) [31]. This is because, apart from the very recent introduction of a chromogenic method, only a single assay method, the onestage clotting assay, has been used for both plasma and concentrates.…”