Measurement of serum theophylline concentrations using a modified Ames TDA system

Results are presented which show that the Ames TDA Theophylline kit provides an accurate and reliable method of measuring the concentration of theophylline in plasma. It may be used with a shortened incubation time (5 min) without loss of accuracy, and a single calibration curve can be used over a 3-week period. There is an acceptable precision at all assayed levels (coefficient of variation, 3.3%) and results obtained for patients' samples correlate well with those obtained using liquid chromatography (y = 0.02 + 1.06x, r = 0.99) and enzyme immunoassay (y = 0.58 + 1.03x, r = 0.99).