[IgG subclass distribution in intravenous immunoglobulin products: determination of reproducibility of a method of IgG subclass determination. Ring Study of the "Plasma Blood Components" Section of the German Society of Transfusion Medicine and Immunohematology].

Background: The working group "Blood Plasma Constituents" of the DGTI has carried out a multicenter study with human immunoglobulins for intravenous administration (IVIG) and a NIBSC serum, with the designation 67/98C, since the European Pharmacopoeia IVIG monograph gives no information for the IgG subclass determination. Aim of the ring study was 1) the determination of the IgG subclass distribution with a standardized method and 2) the determination of the IgG subclass distribution in the NIBSC serum 67/98C and to test if the NIBSC serum coded 67/98C is suited as a reference serum for the IgG subclass determination.

Material and methods: Ten laboratories from Europe participated in the ring study. The IgG subclasses were determined by radial immunodiffusion (RID).

Results: The results showed good consistency between the participating laboratories and showed distinct differences in the IgG subclass composition of the tested IVIGs. The reproducibility of the method showed coefficients of variation of approximately 10%.

Conclusion: The NIBSC serum 67/98C is suitable as reference serum for the IgG subclass determination in sera and IVIGs.