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Clinical Chemistry 53: 985-988, 2007. First published March 29, 2007; 10.1373/clinchem.2007.085316
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(Clinical Chemistry. 2007;53:985-988.)
© 2007 American Association for Clinical Chemistry, Inc.

Technical Briefs

Quantifying Spurious Free T4 Results Attributable to Thyroxine-Binding Proteins in Serum Dialysates and Ultrafiltrates

Kristofer S. Fritz1, R. Bruce Wilcox1 and Jerald C. Nelson2,a

1 Departments of Biochemistry and 2 Internal Medicine and Pathology, Loma Linda University School of Medicine, Loma Linda, CA

aAddress correspondence to this author at: Loma Linda University Medical Center, 11234 Anderson St., Rm. 1568, Loma Linda, CA 92354; fax 909-558-0490; e-mail jcnelson{at}llu.edu


Abstract

Background: Direct equilibrium dialysis and direct ultrafiltration free thyroxine (T4) assays rely on semipermeable membranes to exclude T4-binding serum proteins from dialysates and ultrafiltrates. The presence of these proteins in dialysates or ultrafiltrates will yield spuriously high free T4 values when free T4 is quantified by RIA.

Methods: We used a nonanalog free T4 RIA that detects and quantifies dialyzable and ultrafilterable serum free T4 to detect T4-binding serum proteins. Two equilibrium dialysis devices and 3 ultrafiltration devices were used to illustrate this application. Displacements of [125I]T4 from anti-T4 by various concentrations of T4-depleted thyroxine-binding globulin, albumin, and serum total protein were compared to displacements by various concentrations of free T4.

Results: Both dialysis devices excluded detectable T4-binding serum proteins from dialysates. Two of 3 ultrafiltration devices excluded detectable T4-binding serum proteins from ultrafiltrates. One did not, and its ultrafiltrate yielded spurious free T4 values that correlated directly with serum protein concentrations.

Conclusion: The presence or absence of T4-binding proteins in dialysates and ultrafiltrates and the spurious free T4 values that these proteins cause can be documented using a nonanalog free T4 RIA.




The following articles in journals at HighWire Press have cited this article:


Home page
 Clin. Chem.Home page
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]

Home page
 Clin. Chem.Home page
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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