Method-Specific Variations in the Calibration of a New Immunoglobulin Standard Suitable for Use in Nephelometric Techniques

immunoglobulin standard, IFCC 74/1, was calibrated against the World Health Organization (WHO) immuno-globulin standard 67/99 by three different methods: au-tomated immunoprecipitation, Laurell rocket immunoe-lectrophoresis, and radial immunodiffusion. The same antisera were used in all the assays, which were performed in five expert laboratories. With the aid of linearizing transformations for the dilution curves of both materials and use of a carefully weighted statistical evaluation, values in International Units for lgG, lgA, and 1gM were ascribed to IFCC 74/1. The values achieved by the three different methods were not statistically different, except in the case of IgA. 1gM assays by automated immunopre-cipitation were excluded owing to a high degree of im-precision. Additional Keyphrases: reference standards. intermethcjd comparison. reference values. immunochemistry The uniformity of immunoglobulin measurements between laboratories has been poor in the past (1, 2), owing to differing standard preparations, antisera of differing specificity and affinity, and the use of several different methods. In an attempt to overcome some of these problems, Rowe et a!. (2) assessed the use of a freeze-dried human serum preparation as an immunoglobulin standard by a group of laboratories. When only one method-radial immunodiffusion-was used, reproducibility was con-siderably improved (2). However, agreement between laboratories was far from complete and no satisfactory explanation was found for the residual difference. As a result of this study, the WHO has established international reference preparations of human immu