Automated alarm to detect antigen excess in serum free immunoglobulin light chain kappa and lambda assays

AbstractBackground. Antigen excess causing a falsely low concentration result may occur when measuring serum free immunoglobulin light chains (SFLC). Automated antigen excess detection methods are available only with some analyzers. We have now developed and verified such a method. Methods. Residuals of sera with known SFLC-κ and -λ concentrations were analyzed using Binding Site reagents and methods adapted to the Roche Cobas® c.501 analyzer. Results. We analyzed 117 sera for SFLC-κ and -λ and examined how the absorbance increased with time during the 7 minutes of reaction (absorbance reading points 12–70). From this an antigen excess alarm factor (ratio of absorbance increases between reading points 68–60 and 20–12, multiplied by 100) was defined. Upon our request, Roche added to our two SFLC assays a program which calculated this antigen excess alarm factor and triggered an alarm when the factor was below a defined value. We verified this antigen excess alarm function by analyzing serum from 325 person...