Characterization of an automated radioimmunoassay for T4, T3, T3 U, and FTI

The performance characteristics of assays is reported for thyroxine (T4), triiodothyronine (T3), and T3-uptake (T3U) using the GAMMAFLOTM Automated Assay System. A comparison of calculated free thyroxine index (FTI) values is also presented. This automated radioimmunoassay (RIA) system utilizes a combination of continuous-flow methodology and chromatographic separation techniques. The T4 assay studied had a standard curve range of 1.5 to 24.0 microgram per dl. The intra- and inter-assay precisions were 4.3 and 5.3 percent CV, respectively, for a T4 concentration of 10.0 microgram per dl. The T3 assay had a standard curve range of 50 to 1000 ng per dl, the corresponding precisions were 7.3 and 7.1 percent CV, respectively, for a concentration of 213 ng per dl. The automated serum T4 and T3 results correlated (r = 0.966 and 0.864) with a manual radioimmunoassay procedure. Intra-assay and inter-assay precisions for a mid-range normal 30.1 percent T3U value were 6.2 percent and 4.9 percent CV, respectively. Reference range comparison of FTI by both automated and manual results correlated for 47 out of 51 (95 percent) patients compared. It is concluded that this automated system appears to offer a viable alternative to T4, T3, and T3U manual RIA techniques in terms of operational simplicity, analytical performance, and sample through-put flexibility.