Thyroxine in Serum

L Hemmila, O. Malminen, H. Mikola, and T. Lovgren, Homogeneous time-resolved fluoroimmu-noassay of thyroxin in serum, Clin. Chem. 34, 2320-2322 (1988). 

M6. Miyai, K., Ishibashi, K., and Kawashima, M., Enzyme immunoassay of thyroxine in serum and dried blood samples on filter paper. Endocrinol. Jpn. 27, 375-380 (1980). 

Hemmila, L, Malminen, O., Mikola, H., and Lovgren, T. (1988). Homogeneous Time-Resolved Fluoroimmunoassay of Thyroxine in Serum. Clin. Chem. 34 2320-2322. 

EN19 Danielson, S.J., Brummond, B., Babb, B., Tyminski, P., Birecree, J., Fyles, J. and Pratt, L. (1991). Measurement of total thyroxine in serum or plasma by thin-film enzyme immunoassay. Clin. Chem. 37, 1034, Abstr. 594. 

Danielson S, Warren K, Birecree J, Fyles J, Hermann S, PonticeUo N, et al. Measurement of total thyroxine in serum using a thin-film slide en2yme immunoassay. Clin Chem 1994 40 1024A. 

McDonald LJ, Robin NI, Siegel L. Free thyroxine in serum as estimated by polyacrylamide gel filtration. Clin Chem 1978 24 652-6. 

Peterson B, Hanson R, Giese R, Karger B. Picogram analysis of free triiodothyronine and free thyroxine in serum by equilibrium dialysis and electron capture gas chromatography. J Chromatogr 1976 126 ... 

Until recently it was not always possible to measure unbound thyroxine in serum directly because of the minute quantities involved. Therefore a free thyroxine index calculation was often made, since this value is proportional to the free thyroxine concentration. This index can be arrived at by multiplying a measure of thyroxine in the blood (usually the FBI) by a value derived from the measurement of thyroxine-unoccupied binding sites of thyroxine-binding proteins. This was possible since the uptake of thyroxine or triiodothyronine by red cells or resin is inversely proportional to the number of unoccupied binding sites. As thyroxine-binding sites become increasingly saturated, the free thyroxine levels increase. An example of this method of arriving at a free thyroxine index is the work of Clark and Horn (C5). Calculation of the free thyroxine index is valuable since the FBI determination and the resin uptake of Ts are determinations that are routinely made in many clinical laboratories. 

L5. Liewendahl, K., and Lamberg, B.-A., Free thyroxine in serum determined by dialysis and Sephadex G-25 filtration. J. Clin. Endocrinol. Metab. 26, 991-993 (1965). 

C13. Christensen, L. K., A method for determination of free, non-protein bound thyroxine in serum. Scand. J. Clin. Lab. Invest. 11, 326-331 (1959). 

Schussler, G. C., and Plager, J. E., Eifect of preliminary purification of 1-thyroxine on the determination of free thyroxine in serum. J. Clin. Endocrinol. Metab. 27, 242-250 (1967). 

Spaulding, S. W., and Gregerman, R. I., Free thyroxine in serum by equilibrium dialysis Effects of dilution, specific ions and inhibitors of binding. /. Clin. Endocrinol. Metab. 34, 974-982 (1972). 

W12. Wellby, M. L., O Halloran, M. W., and Marshall, J., A comparison of effective thyroxine ratio and free thyroxine in serum. Clin. Chim, Acta 45, 255-259... 

A fifth group of procedures includes the use of an array format. The usual 96-well plate for immunoassay measures the fluorescence in liquid phase either by determining the unbound fraction or by dissolving the bound reporter molecules to overcome problems related to autofluorescence, scattering, and back-reflection, although the selection of an appropriate solid support allows for the measurement of the fluorescence directly on the solid surface. For example, a heterogeneous fluoroimmunoassay using fluorescein-labeled antibodies for total thyroxin in serum uses this procedure. 

Measurement of the free (physiologically active) thyroxine in serum. This may be determined directly or can be derived (the free thyroxine index) if a T3 resin uptake or a thyroxine-binding globulin level is measured. 

From 1968 to 1975 the distributioon of iodized salt was silently interrupted in 2 small districts (Podoba, unpublished). Within one year the urinary iodine decreased from about 100 g/24h to about 40 fiq/2 h. In addition, the total iodine in thyroid and thyroxine in serum decreased, while uptake by thyroid and thyrotropin in serum increased. 

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