A RATE TURBIDIMETRIC IMMUNOASSAY FOR THEOPHYLLINE USING BIOTIN-AVIDINSYSTEM

We describe a biotin-avidin based rate turbidimetric homogeneous immun oassay for the determination of serum theophylline with a measuring ra nge of 0-40 mug/ml. The assay features an avidin-biotin-labeled theoph ylline conjugate and a monoclonal antibody. The rate of change of turb idity caused by the antibody-conjugate complexing was monitored on the Beckman Synchron CX(R) 4 System at 340 nm and 37-degrees-C. Theophyll ine in a sample inhibited the complexation, and the extent of inhibiti on allowed the quantitation of theophylline in the sample. The within- run coefficient of variation (CV) was < 3.7% and the between-run CV wa s 5.2-9.2% depending on the theophylline concentration. Linear regress ion analysis showed a good correlation with an established fluorescenc e polarization immunoassay (r = 0.9866, n = 94).