Evaluation of fluorescence polarization immunoassay for serum thyroxine determination.

We have evaluated a fluorescence polarization immunoassay for thyroxine (T4) using the polarization analyzer IBF-129. Fluorescence polarization could be measured within 20 to 23 seconds after addition of fluorescein labeled thyroxine. The method exhibited excellent specificity and acceptable accuracy. The average intra- and inter-assay coefficients of variation were 4.8 and 12.3%, resepectively. The fluorescence polarization immunoassay was compared with a radioimmunoassay (RIA) using 96 clinical serum samples and gave a linear regression equation: y = 0.92 x + 12.5, with a correlation coefficient of r = 0.866 (P less than 0.001).