Summary
An international collaborative study, involving 18 laboratories, was carried out to
establish an international standard for protein C in plasma. The proposed standard,
which consisted of a freeze-dried ampouled plasma preparation coded 86/622, was assayed
against fresh normal plasma and the participants’ local standards. Protein C activity
assays were placed in four groups, depending on the method of activation and detection
of protein C. The combined potencies (units per ampoule) for the proposed international
standard were: thrombin activation/clottirg assays, 0.86; thrombin activation/chromogenic
assays, 0.81; snake venom activation/clotting assays, 0.81 and snake venom activation/chromogenic
assays, 0.82. Measurement of protein C antigen gave potency estimates of 0.81 and
0.82 units per ampoule for the Laurell electroimmunoassay and ELISA techniques, respectively.
The good agreement in potency estimates between the different methods indicates that
the overall combined figure (226 assays) for the international standard of 0.82 international
units per ampoule should serve for all methods. Accelerated degradation studies have
indicated that the standard should be suitably stable when stored at −20° C.
The freeze-dried plasma 86/622 has been established by the WHO Expert Committee on
Biological Standardization as the 1st International Standard for Protein C in Plasma,
with an assigned unitage of 0.82 international units per ampoule.
Keywords
Protein C - Plasma - Internatibnal Standard
