Optimizing nephelometric measurement of specific serum proteins: evaluation of three diluents.

Three diluents were studied, to determine which is the best for the automated immunochemical measurement of specific serum proteins. Nine serum proteins (orosomucoid, a 1-antitrypsin, a2-macroglobulin, haptoglobin, transferrin, C3, lgG, IgA, and 1gM) were measured in physiological saline (9 g NaCI/liter), tris(hydroxymethyl)aminomethane buffer (0.01 mol/liter; pH 7.4), and physiological saline containing polyethylene glycol (‘PEG 6000,” 40 g/liter). Criteria were: reaction rate, analysis rate, carryover between samples, steady-state approximation, precision, and correlation with other methods. Saline containing polyethylene giycol is the best of the three diluents for use in continuous-flow nephelometric analysis of serum proteins.