If the sum of the 4 IgG subclasses differs by >20% from the total IgG concentration, the assays are repeated at higher dilutions to rule out
antigen excess. During our validation studies, serum from an 82-year-old male was submitted for subclass quantification.
WHAT IS THE PREVALENCE OF
ANTIGEN EXCESS IN THE FLC ASSAY?
In conclusion, both nephelometric methods for urinary FLCs were objective and reproducible and identified those samples containing high concentrations of monoclonal FLCs without
antigen excess problems.
This procedure with the 0.200 cutoff value for the prozone check effectively detected all samples in which
antigen excess caused falsely low microalbuminuric or normal values.
We were careful to characterize our procedure regarding
antigen excess, a prozone artifact that can occur with IFE (19).
The imbalance of antigenic determinants between polyclonal and monoclonal light chains makes methods susceptible to the risk of
antigen excess. Problems of
antigen excess occur, with even robust immunoassays for total light chains yielding falsely low light-chain concentrations and thus missing the diagnosis of potentially serious conditions such as light chain myeloma or light chain amyloidosis.
The purpose of this study was to evaluate the analytical performance of these Abbott Aeroset specific-protein assays and, in particular, their ability to correctly handle
antigen excess frequently found in immunoglobulin estimations.
To verify that an assay does not give falsely low results in the presence of the very high concentrations of PSA or FPSA that may be present in human samples (
antigen excess or hook effect), aliquots of the zero calibrator containing PSA concentrations of 19-625 000 [micro]g/L and FPSA concentrations of 5-160 000 [micro]g/L were prepared by the manufacturer.
Furthermore, this simple prozone detection method can be adapted to other nephelometric assays with the potential for erroneous results from
antigen excess.
