Automated alarm to detect antigen excess in serum free immunoglobulin light chain kappa and lambda assays - Experience from routine application.

Karin Toska1,*, Erik Koldberg Amundsen1, Petter Urdal1, Olav Klingenberg1

1Department of Medical Biokjemistry, Oslo University Hospital, Oslo, Norway

Introduction: Antigen excess occurs when antibody of a defined limited capacity is mixed with too high amount of antigen, causing a false, mostly low concentration result. We have recently developed and verified an automated antigen excess detection method (prozone check) for use with an immunological assays for serum free immunoglobulin light chains, SFLC-k and SFLC-l,  using Binding Site reagents and methods adapted to the Roche Cobas c.501 analyzer (1).

Objectives: In order to detect any lot-to-lot reagent differences in appropriate cut-off level of the alarm, we follow the SFLC antigen excess alarm factor (AEAF) values and its relationship to the SFLC concentrations during routine use during a 6 month period. 

Methods: The antigen excess method is based on recordings of absorbance development during the initial seven minutes of reaction (absorbance reading points 12-70) in patient sera, with and without antigen excess. The AEAF is calculated as the ratio of absorbance increases between reading points 60-68 and 12-20, multiplied by 100. 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 outside a defined value range. This alarm initiates an automatic rerun at a five-fold lower sample fraction. The AEAF was subsequently verified by analyzing serum from 325 persons of whom 143 were multiple myeloma patients. The AEAF did detect all known antigen excess samples. In the present study, we follow the value of AEAF and the resulting value of the concentration results from the daily, routine use in all samples sent to the department of medical biochemistry for analysis of SFLC. Daily control sera and several of frozen sera with known AEAF from the previous study were also analyzed.

Results: Will be presented

Conclusion: An AEAF based on the absorbance development during antigen-antibody reaction is able to detect antigen excess in SFLC analysis. 

Keywords: Biochemistry, Method