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Clinical Chemistry, Vol 29, 816-822, Copyright © 1983 by American Association for Clinical Chemistry
T Helenius and K Liewendahl
We describe a method for free thyroxin (FT4) in serum, based on radioimmunoassay of T4 in serum dialysate, FT4(D). The method is analytically accurate, sensitive, reproducible, and suitable for routine use in the clinical laboratory. We compared results by this method with those obtained with five commercial FT4 assays (Amerlex, GammaCoat, ImmoPhase, LiquiSol, Spiria) and the free T4 index (FT4I). In several of the patients with nonthyroidal illness FT4(D) was above normal and FT4 as measured with the commercial assays was subnormal. In the third trimester of pregnancy all the FT4 methods gave decreased mean values, though the decreases were of various magnitudes: FT4(D) 32%, Amerlex 44%, GammaCoat 40%, Spiria 19%, LiquiSol 16%, and ImmoPhase 13%, respectively. FT4I was significantly higher than normal during late pregnancy. In women taking oral contraceptives the mean FT4I was increased, but there was no significant effect on the results obtained with the various FT4 methods. All subjects with hereditarily high or low serum thyroxin-binding globulin had normal FT4(D) and abnormal FT4I. Amerlex, ImmoPhase, and LiquiSol misclassified some of the subjects with hereditarily abnormal thyroxin-binding globulin.
The following articles in journals at HighWire Press have cited this article:
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  B. Yue, A. L. Rockwood, T. Sandrock, S. L. La'ulu, M. M. Kushnir, and A. W. Meikle Free Thyroid Hormones in Serum by Direct Equilibrium Dialysis and Online Solid-Phase Extraction-Liquid Chromatography/Tandem Mass Spectrometry Clin. Chem., April 1, 2008; 54(4): 642 - 651. [Abstract] [Full Text] [PDF]
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K. S. Fritz, R. B. Wilcox, and J. C. Nelson A Direct Free Thyroxine (T4) Immunoassay with the Characteristics of a Total T4 Immunoassay Clin. Chem., May 1, 2007; 53(5): 911 - 915. [Abstract] [Full Text] [PDF]
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K. S. Fritz, R. B. Wilcox, and J. C. Nelson Quantifying Spurious Free T4 Results Attributable to Thyroxine-Binding Proteins in Serum Dialysates and Ultrafiltrates Clin. Chem., May 1, 2007; 53(5): 985 - 988. [Abstract] [Full Text] [PDF]
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K. Van Uytfanghe, D. Stockl, H A. Ross, and L. M. Thienpont Use of Frozen Sera for FT4 Standardization: Investigation by Equilibrium Dialysis Combined with Isotope Dilution-Mass Spectrometry and Immunoassay Clin. Chem., September 1, 2006; 52(9): 1817 - 1821. [Abstract] [Full Text] [PDF]
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S. S. Holm, L. Andreasen, S. H. Hansen, J. Faber, and P. Staun-Olsen Influence of Adsorption and Deproteination on Potential Free Thyroxine Reference Methods Clin. Chem., January 1, 2002; 48(1): 108 - 114. [Abstract] [Full Text] [PDF]
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J. E.M. Midgley Direct and Indirect Free Thyroxine Assay Methods: Theory and Practice Clin. Chem., August 1, 2001; 47(8): 1353 - 1363. [Abstract] [Full Text] [PDF]
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N. D. Christofides, E. Wilkinson, M. Stoddart, D. C. Ray, and G. J. Beckett Assessment of Serum Thyroxine Binding Capacity-dependent Biases in Free Thyroxine Assays Clin. Chem., April 1, 1999; 45(4): 520 - 525. [Abstract] [Full Text] [PDF]
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 D. Glinoer The Regulation of Thyroid Function in Pregnancy: Pathways of Endocrine Adaptation from Physiology to Pathology Endocr. Rev., June 1, 1997; 18(3): 404 - 433. [Abstract] [Full Text]
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