Immunoassay for serum thyroxine monitored by chemiluminescence.

An immunoassay for thyroxine (T4) monitored by chemiluminescence was evaluated with clinical serums. A thyroxine-label conjugate (T4-L) and serum samples were applied sequentially to alkaline Sephadex G-25 columns which adsorbed the thyroxine species. Other serum components and potential interferents were washed from the column with barbital buffer. Subsequently addition of antibody initiated the binding reaction. After 1 h incubation, the antibody was eluted from the column with a barbital buffer wash. The bound T4-L in the eluate was oxidized in a chemiluminescent detection reaction. The peak light intensity, attained in about 1 sec, was related to T4 concentration by means of standards. The intra-assay precision of the chemiluminescence immunoassay was +/-5% (C.V.). Statistical comparison of T4 levels determined for 28 serums by this method and a reference assay was acceptable (y = 0.95x + 5.9, r = 0.98, Sy square root of y . 100 = 13.1%).