AN ENZYME-IMMUNOASSAY FOR TOTAL THYROXINE USING AVIDIN-BIOTIN SEPARATION SYSTEM AND THYROXINE-PEROXIDASE CONJUGATE

An avidin-biotin enzymeimmunoassay for total thyroxine in serum is des cribed. Avidin was adsorbed to biotinylated bovine serum albumin coate d tubes prepared with glutaraldehyde as coupling agent. In the enzymei mmunoassay, affinity purified biotinylated anti-thyroxine IgG, sample or standards, and thyroxine-horseradish peroxidase were simultaneously added to the avidin coated tubes. The bound enzymatic activity was th en measured with o-phenylenediamine and H2O2. Results showed that the assay has good precision (within-assay CV% less than 10% and between a ssay 11.7% in hypo- and 6.9% in hyperthyroid range), good assay range (0-800 nmol/L), good sensitivity (4 nmol/L), and can be performed in 2 .5 hours. The results obtained correlate well (r=0.93) with those of a n RIA.