Performance characteristics of four immunonephelometric assays for the quantitative determination of IgA and IgM in cerebrospinal fluid

Measurement of IgA and IgM in cerebrospinal fluid (CSF) can be useful in the diagnosis of multiple sclerosis and other central nervous system disorders. The Dade Behring (Deerfield, IL) N Latex IgA and N Latex IgM tests on the BN H System and Beckman Coulter (Brea, CA) low-concentration IgA and IgM tests on the IMMAGE Immunochemistry System were evaluated for linearity, imprecision, method comparison, and reference interval verification. Both IgA methods were linear from 1.4 to at least 50 mg/L. Both IgM method were linear from 0.14 to more than 6 mg/L. The total imprecision of the BN II IgA and IgM methods and the IMMAGE IgA method was less than 10%. The imprecision of the IMMAGE IgM method was 10.2% at 0.49 mg/L and less than 5% at higher IgM concentrations. Method comparison studies indicated that IgA and IgM methods on both instruments showed good comparability. Reference interval studies demonstrated that both methods had similar reference intervals that agreed with published values of less than 6 mg/L for IgA and less than 1.3 mg/L for IgM. Methods for quantifying IgA and IgM in CSF on the BN II and IMMAGE nephelometers perform well and give comparable results.