Quality of commercially available controls in laser immunonephelometry

Lack of accuracy in expressing concentrations of specific proteins in different lots of Hyland calibrating reference and quality control materials, supplied for the Hyland PDQ laser nephelometer, prompted an attempt to find alternative and more reliable calibrating materials available commercially. Laser grade (Atlantic Antibodies) and radial immunodiffusion grade materials (Behring Diagnostics) were evaluated in this study. Using Atlantic Antibodies' calibrator, only five of 11 specific proteins assayed in Atlantic control serum were within acceptable ranges; precision was less than that using Hyland materials of identical lots. Mean values for each of 10 of the same 11 specific proteins of Behring control plasma assayed against Behring stabilised human serum, were within manufacturers' acceptable ranges; however, precision was less than that with Hyland materials from identical lots. Nine of the 11 specific proteins in a frozen serum pool sample, measured on the laser nephelometer, agreed well with results of the specific proteins measured by radial immunodiffusion, using the same Behring calibration and quality control. Only the Hyland materials were prediluted for use, which explains the greater precision that was obtained. Intercomparison of concentrations, as expressed by respective manufacturers, was largely unacceptable. Based on these results there is need, until satisfactory reagents become available, to standardise on one parent Hyland reference sample giving best precision and to calibrate all subsequent working standards against the parent reference.