Evaluation of Enzyme Immunoassays for Determination of Thyroxine (EMIT, ENZYMUN) and of Thyroxine Binding Index

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Abstract
An evaluation of enzyme immunoassays for determination of thyroxine in serum (EMIT [enzyme multiplied immunoassay technique] ABA thyroxine assay, Syva Corp., ENZYMUN [based on the enzyme-linked immunosorbent assay], Boehringer Mannheim) and of thyroxine binding index (ENZYMUN assay TBI, Boehringer Mannheim) is presented. The precision of the enzyme immunoassays was adequate (coefficients of variation (cv) ranged from day to day with EMIT from 3-11% and with ENZYMUN from 4-11%). Both assays are specific and easy to perform. About 20 unknown samples can be analyzed in duplicate by EMIT within 60 min and by ENZYMUN within 250 min. A comparison of the results obtained by enzyme immunoassays and radioimmunoassay in a series of .apprx. 100 patients showed a good correlation between both methods. The precision of the ENZYMUN TBI assay was adequate (cv from day to day 4.9%) and the thyroxine/TBI-ratio correlated well with the thyroxine/TBG[thyroxine-binding globulin]-ratio.
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