We conclude that the quantification of IgG subclasses by LC-MS/MS using isotope-labeled ISs specific for each subclass or a surrogate digestion standard (horse IgG) has similar performance to current nephelometric-based assays and is not subject to antigen excess
Some nephelometers, including the BN II, have automated detection algorithms designed to detect antigen excess.
In samples that are not in antigen excess, the 400-fold dilutions give concentrations that are 50% higher on average than those obtained with the 100-fold dilutions.
Because of the potential for [kappa] FLC antigen excess, newly identified cases with abnormally high ratios should be retested with a further dilution.
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
Any sample that does not dilute properly may have antigen excess.
With this protocol, we have found two samples, one for prostate-specific antigen (PSA) and one for CA-125, with falsely low values attributable to antigen excess.
We report the development of a sensitive and reliable method for urine albumin measurement on the Dade aca[R] that has excellent calibration and reagent stability and no problems caused by antigen excess.
The choice of the inhibition format provides good sensitivity at the low analyte concentration with an avoidance of antigen excess possibilities, while the covalent coupling of albumin to the particles ensures that the particle reagent is stable; this characteristic has been demonstrated for other immunoassays where covalent coupling of protein was used [22-24].
Furthermore, this method offers the security of avoidance of the risks of antigen excess by use of the inhibition format.