Fluorescence polarization immunoassay for theophylline modified for use with dried blood spots on filter paper

We used dried blood spots successfully as alternative specimens for quantifying concentrations of theophylline in 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 Sxy = 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.