A fluorescent immunoassay for theophylline: description and comparison to enzyme immunoassay, liquid chromatography and radioimmunoassay

A fluorescent immunoassay for theophylline is described and comparatively evaluated with radioimmunoassay, high-performance liquid chromatography, and enzyme immunoassay. Fifty sera were collected from 43 patients of a large acute-care medical facility, many of whom were suffering from other diseases in addition to bronchial asthma or apnea of the newborn, and were receiving other medication besides theophylline. Assays of theophylline in each serum sample were performed by each of the 4 procedures. The four methods showed comparable results, although each method had at least one unexplained outlier. Nevertheless, all methods seemed suitable for routine chemistry laboratory use. Three of the techniques have been available for several years, but unexplained erroneous levels are sometimes obtained for every procedure.