Total thyroxine

Sample material Serum or plasma (EDTA or heparin). Oxalate and citrate are not suitable as anticoagulants for plasma separation, since the thyroxine concentration may be reduced. Serum and plasma samples can be stored in the refrigerator at +2°C to +8°C for one week. 

Specificity The specificity of the antiserum was tested with substances having a structure similar to that of thyroxine. 

Interferences Haemolytic (haemoglobin up to 12 g/1), lipaemic (triglycerides up to 2450 mg/1, cholesterol up to 500 mg/dl) and icteric (bilirubin up to 5 mg/dl) samples do not produce any clinically significant effect. 

References Packing leaflet LI 0622-D 1/87, LIM 0622-M 10/89, ST8, ST13, ST17, ST25, ST35, ST45. 

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Triiodothyronine, total thyroxine, thyroxine uptake, and thyroid-stimulating hormone. 

Estrogen may increase hepatic production of thyroxine-binding globulin (TBG) and decrease TBG clearance, thus increasing serum total thyroxine (tT4) and, to a lesser extent, total triiodothyronine (tT3). As a result, increased tT4 and tT3 are seen in states of excessive estrogen and/or progestin, such as... 

Oral contraceptives can cause an increase in total thyroxine (163) and a fall in the percentage of free thyroxine (164). The uptake of radioactive iodine in the thyroid is usually normal total uptake of radioactive iodine may be reduced (164). The effect of progestogens on thyroxinebinding globulin may possibly counteract the estrogenic action. The net result will be a rise in protein-bound iodine and a fall in resin triiodothyronine uptake (165). It has been suggested that oral contraceptives may actually have some protective effect against thyroid disease. 

Recently it was shown by Darnerud and Sinjari [286a] that 2,2, 4,4 -tetrabro-modiphenyl ether decreased the total thyroxine plasma levels in rats and mice... 

Administration of 4-OH-3,3, 4, 5-tetrachlorobiphenyl and 4-OH-CB107 to pregnant mice reduced the total thyroxine levels in both maternal and fetal plasma [34]. However, the decrease was less dramatic when the CB-77 was administered alone, and the metabolite formed in vivo [197]. Administration of Aroclor 1254 to adult rats resulted in high OH-PCB levels in plasma and a concomitant reduction in thyroxine [198]. In fetal and weanling rats, similar... 

Artefactual increases of as much as 50% in total thyroxine, estimated by a competitive protein-binding assay, and of as much as 30% in triiodothyronine resin uptake are probably due to rapid and continuing lipolytic hydrolysis of triglycerides after blood has been drawn (126). Thyroid function tests should therefore always be performed on blood samples taken before (or a sufficient time after) heparin treatment (127). An increase in serum-free thyroxine concentrations has also been reported after low molecular weight heparin, by up to 171% in specimens taken 2-6 hours after injection. When specimens were obtained 10 hours after injection, the effects were smaller, but with concentrations still up to 40% above normal the results can still cause errors of interpretation (128). 

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. 

Other reagent carriers have been presented in the literature, which, however, are not yet commercially available. First reports have been published on albumin (S17), calcium (S14), quinidine (S85, S187), total protein (S22), total thyroxine (S231), free thyroxine (S273), lidocaine (S84), primidone (S20) and valproic acid (SI74). 

S231 Fredrickson, R.A., Belchak, T.L., Foltz, M.M., Loeschen, B.J., Profitt, J.A., Yoder, J.M. and Morris, D.L. (1989). An immunometric total thyroxine assay for use with dry reagent strips and a reflectance photometer. Clin. Chem. 35, 1140-1141, Abstr. 353. 

ST32 Stahlschmidt, G.E., Smith, S.H., Miller, R.E. and Landt, M.L. (1987). The Stratus fluorometric enzyme immunoassay system evaluated for the determination of total thyroxine. Clin. Chem. 33, 883, Abstr. 17. 

Sojka J E, Johnson M A, Bottoms G D 1993 Serum triiodothyronine, total thyroxine, and free thyroxine concentrations in horses. American Journal of Veterinary Research 54 52-55 Medical Economics Staff, PDR Staff and Physicians 2002 Physician s Desk Reference 2003, 57th edn. Thompson Healthcare, Montrale, NJ, pp. 569-571 Williams P D 1995 Equine Cushing s syndrome ... 

Plasma growth hormone concentration may rise by as much as 15 times at the start of a fast but may return to normal after 3 days. Reduced energy expenditure is associated with decreased concentrations of thyroid hormones. Free and total triiodothyronine decrease by up to 50% witliin 3 days of the start of a fast. Free thyroxine concentration is also affected, but to a lesser extent total thyroxine is little changed. Urinary free cortisol is decreased by fasting, and the plasma cortisol concentration (free and total) shows a slight increase together with loss of the normal diurnal variation. 

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. 

Greene H, Hwang D, Hutchins J, Johnson A. Techni-con thyroxine and thyroid binding globulin Two fuHy automated immunoassays for the determination of total thyroxine and TBG in human serum, Clin Chem 1990 36 1082. 

Hayes E, Sunonaitis R, et al. An automated chemiluminescence immunoassay test for total thyroxin. Clin Chem 1991 37 942. 

Nelson JC> Wilcox RB. Analytical performance of free and total thyroxine assays. Clin Chem, 1996 42 146-54. 

Serum creatinine, blood urea nitrogen, urinalysis, urine osmolality, specific gravity, triiodothyronine, total thyroxine, thyroxine uptake, and thyroid-stimulating hormone. 

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