A rapid laser immunonephelometric assay for serum amyloid A (SAA) and its application to the diagnosis of kidney allograft rejection.

We set up a laser nephelometric assay for the quantitation of serum amyloid A (SAA) in human plasma. Therefore monospecific antibodies were raised in sheep and used in parallel to measure SAA concentrations by nephelometry and also by radial immunodiffusion, an assay usually applied for determination of SAA. The nephelometric method is precise, simple and unlike radial immunodiffusion results are obtained within an hour. The antigen concentrations determined both by laser nephelometry and radial immunodiffusion correlated highly (r = 0.98). As plasma SAA concentrations were reported to be a possible marker of kidney allograft rejection, the assay was applied to measure SAA concentrations in patients after kidney transplantation. Data were compared with clinical and other biochemical parameters. The period after kidney transplantation is reported for two cases, where SAA plasma concentrations were helpful in diagnosing allograft rejection. The rapid availability of the SAA plasma concentrations by nephelometry makes them a possible additional tool to decide quickly upon antirejection therapy.