Table 1. Tdx Settings for Dbs-theophylllne Fluorescencepolarizationimmunoassayfortheophyllinemodifiedfor Use with Driedbloodspotson Filterpaper Materials and Methods Instrumentation

We used dried blood spots successfully as alternative specimens for quantifyingconcentrationsof theophyllinein the circulation by a modified fluorescence polarization immunoassay (FPIA) with the Abbott TDx instrument. The method described is simple, rapid, and acceptably precise. More importantly, it can provide results comparable with those of the conventional serum assay. Results for 64 pairs of dried blood spots (y and serum (x) specimens analyzed by the respective FPIA methods yielded the following regression parameters: y = 0.94x + 0.71, r = 0.988, and S,, = 0.92. A major advantage of FPIA is that it requires only basic laboratory skills. When coupled with the use of dried blood spots, this system can be effective in remote theophylline monitoring, particularly suited for domiciliary care.