Evaluation of Particle-Enhanced Turbidimetric Inhibition Immunoassay for Determination of Theophylline Concentration in Serum

(Received April 30, 1987) We evaluated the particle-enhanced turbidimetric inhibition immunoassay (PETINIA) for the measurement of theophylline in serum. The coefficients of variation in both within-day (n= 10) and between-day (n=10) precision studies were less than 4 %, and the analytical recoveries were 98-103% at the concentrations of 5, 10 and 20 Pg/ml of theophylline. Good correlations were observed among assay results by PETINIA, high-performance liquid chromatography (HPLC) and fluorescence polarization immunoassay (FPIA) for 120 serum specimens cbllected from patients with chronic obstructive pulmonary disease receiving theophylline therapy. The regression lines obtained were : PETINIA =1.034 x HPLC -0.404 (r =0.994, Sy/x=0. 57Pg/ ml), PETINIA =1.037 x FPIA0.539 (r=0.995, Sy/x=0.51pg/m1). The cross reactivity in PETINIA was also studied with 11 compounds structurally related to theophylline. None of these compounds exhibited significant cross reactivity (less than 5 %) except for 1,3-dimethyluric acid (11%). From these results, we could conclude that PETINIA is a useful method for therapeutic monitoring of serum theophylline having good precision and accuracy, and high specificity.