A reagent strip for the quantitative analysis of theophylline in serum or plasma was evaluated. The strip is based on the apoenzyme reactivation immunoassay system (ARIS) technique and is intended for use with the Ames Seralyzer reflectance photometer. The method gave CVs at three theophylline levels ranging from 3.8 to 6.3percnt; (within run) and from 2.8 to 6.9percnt; (day to day). The regression lines obtained from the correlation studies were y = 0.959x plus; 0.51 (n = 105, r = 0.9906, Sy/x= 0.56) for the comparison ARIS (y) versus Syva enzyme multiplied immunoassay (x) methods, and y = 0.986x plus; 0.32 (n = 105, r = 0.9832, Sy/x= 0.62) for the comparison ARIS (y) versus Abbott TDx fluorescence polarization immunoassay (x) methods. The interference from triglycerides, hemoglobin, bilirubin, and ascorbic acid, and the cross-reactivity of 8-chlorotheophylline, caffeine, 1,3-dimethyluric acid, theobromine, and 1,7-dimethylxanthine, were also investigated and discussed. The method was found to be reliable, simple, and rapid. It provides a practicable solution for immediate determinations of theophylline.
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