A self-contained light-scattering accessory carousel has been developed for the Abbott TDx fluorescence polarization analyzer, extending the instrument's capabilities to nephelometric methods of analysis, including assays for specific proteins by immunoprecipitation: IgG, IgA, IgM, and transferrin. The scattered light from a green-light-emitting diode (peak wavelength 565 nm) is measured at an angle of 37.5 degrees by the existing optical detection system of the TDx analyzer without modification of the instrument. Measurements are made at quasi-equilibrium, with sample blank correction. No sample pretreatment is required, and antigen-excess is checked automatically. CVs range from 3 to 6% (within-run) and 7 to 9%. (total). Calibration curves may be stored for at least two weeks. A nephelometric method for monitoring chromogenic reactions in the green wavelength region is also described. This method--Scattered Energy Attenuation (SEA)--has been used in preliminary experiments to measure calcium, total protein, iron, and bilirubin.

We critically evaluated the Nephelometry System (TDx Turbo) for the TDx Analyzer (Turbo), as currently used for immunoglobulins (IgA, IgG, and IgM) and transferrin assays. We describe hardware, software, reagent, and procedural changes made since the original publication (Clin Chem 1985;31:1474) and the mathematical treatment of data. The unit-dose format of the reagents allows for batch or panel testing of the analytes, with a throughput of 40 tests per hour. Measurements are made at pseudo-equilibrium, with sample-blank correction. The formulation of reagents and the assay scheme are such as to eliminate the need to check these assays for antigen excess. Assay sensitivities are 3% of the standard curve ranges. CVs are 8% for all assays. The system performance, when compared with rate nephelometry and radial immunodiffusion, yielded correlation coefficients of 0.97 or better for the analytes.

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