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Clinical Chemistry, Vol 36, 800-804, Copyright © 1990 by American Association for Clinical Chemistry
SH Tikanoja and BK Liewendahl
Kuopio University Central Hospital, Finland.
This new ultrafiltration method for free thyroxin in serum [FT4(U)] is based on radioimmunoassay of the free hormone fraction in ultrafiltrates obtained by centrifuging serum samples in Unisep Ultracent-10 ultrafiltration devices. We compared the results obtained with those by an equilibrium dialysis method [FT4(D)]. In 36 euthyroid healthy subjects, the mean FT4(U) concentration was 24.2 pmol/L and the mean FT4(D) concentration 14.8 pmol/L. In hyperthyroid and hypothyroid patients, results by the ultrafiltration method were also approximately twice as high as those obtained by the dialysis method. In 23 patients with various nonthyroidal illnesses, mean FT4(U) was 41.2 pmol/L and mean FT4(D) 19.8 pmol/L. The mean FT4(U)/FT4(D) ratio in patients with nonthyroidal illnesses (1.97) was not significantly higher than in control subjects (1.68), making it unlikely that the increase in serum FT4 is caused by weakly protein-bound and therefore dialyzable inhibitors of thyroxin binding to carrier proteins. However, two nonthyroidally ill patients with a clearly increased FT4(U) but a normal FT4(D) concentration might have had such inhibitors, whereas for two other nonthyroidally ill patients a high molar ratio of free fatty acids to albumin is a more likely explanation for increased FT4(U) and FT4(D) concentrations. On theoretical grounds, we consider the FT4(U) concentrations analytically more nearly accurate than FT4(D) values for all patient groups studied.
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. M. Weiss, J. C. Nelson, and R. B. Wilcox Unequal Concentrations of Free T3 and Free T4 after Ultrafiltration Clin. Chem., July 1, 2007; 53(7): 1384 - 1385. [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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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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