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Clinical Chemistry 31: 517-522, 1985;
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Clinical Chemistry, Vol 31, 517-522, Copyright © 1985 by American Association for Clinical Chemistry

Improved ultrafiltration method for simultaneous measurement of free thyroxin and free triiodothyronine in serum

YS Wang, JM Hershman and AE Pekary

We describe a new ultrafiltration method for measuring concentrations of free thyroxin (FT4) and free triiodothyronine (FT3). Serum containing [131I]T4 and [125I]T3 is diluted 10-fold in phosphate buffer (500 mmol/L, pH 7.4 at 37 degrees C), then passed through a YMT membrane in an Amicon MPS-1 centrifugal ultrafiltration device. Radioactive iodide and protein-bound thyronines are separated from FT4 and FT3 in the ultrafiltrate by use of a Sephadex G-25 microcolumn. In normal controls, the fraction of T4 that passes into the ultrafiltrate is 0.021 +/- 0.006% (mean +/- SD), FT4 is 19.6 +/- 6.5 ng/L, the fraction of T3 that passes into the ultrafiltrate is 0.18 +/- 0.5%, and the FT3 is 2.03 +/- 0.50 ng/L. Intra-assay precision (CV) is 5.4% for FT4 and 4.2% for FT3; the respective interassay CVs are 10.1% and 8.0%. In various groups of patients with thyroid disease and other conditions that influence serum T4 and T3 concentrations, FT4 by ultrafiltration correlated with FT4 measured by equilibrium dialysis (r = 0.84, p less than 0.001) and FT3 by ultrafiltration correlated with FT3 measured by the Diagnostic Products RIA kit (r = 0.87, p less than 0.001). The accuracy, reproducibility, speed, and simplicity of the ultrafiltration method compared favorably with the more cumbersome method of equilibrium dialysis.


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


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 Clin. Chem.Home page
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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L. J. De Groot
Dangerous Dogmas in Medicine: The Nonthyroidal Illness Syndrome
J. Clin. Endocrinol. Metab., January 1, 1999; 84(1): 151 - 164.
[Full Text]


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