Standardization for four protein analytes with the Behring Nephelometer

Owing to the generally higher values observed in the initial establishment of immunoglobulins (Ig) G, A, and M assays with the Behring Nephelometer, we elected to verify five commercial protein calibrators. This initial verification was performed by standardizing the Behring Nephelometer with the World Health Organization (WHO) International Reference Preparation for Human Serum Immunoglobulins G, A, and M. The instrument was also standardized for immunoglobulins and transferrin with use of the Reference Preparation for Serum Proteins (RPSP II). Analytical recoveries of the commercial calibrators varied. Also, assigned protein concentrations in both the WHO and RPSP II preparations made them unacceptable to us as benchmark calibrators for the Behring Nephelometer. Individual proteins (IgG, IgA, IgM, and transferrin) were obtained and primary standards prepared. Both transferrin and IgG were successfully standardized. However, IgA and IgM primary standards lacked 100% antigenicity, requiring removal of nonreactive IgA and IgM or reassignment of the correct value. The problem remains to find appropriate purified materials for IgA and IgM standardization.