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THE GENERATION DIAGNOSTIC SYSTEM
3,5,3' Triiodothyronine (T3) is a thyroid hormone with a molecular weight of 651 daltons. T3 circulates in the blood as an equilibrium mixture of free and protein bound hormone. T3 is bound to thyroxin binding globulin (TBG), prealbumin, and albumin. The actual distribution of T3 among these binding proteins is controversial as estimates range from 38-80% for TBG, 9-27% for prealbumin, and 11-35% for albumin. T3 plays an important role in the maintenance of the euthyroid state. T3 measurements can be a valuable component in diagnosing certain disorders of thyroid function. Most reports indicate that T3 levels distinguish clearly between euthyroid and hyperthyroid subjects, but provide a less clear-cut separation between hypothyroid and euthyroid subjects. Total T3 measurements may be valuable when hyperthyroidism is suspected and the free T4 is normal. For example, one recognized type of thyroid dysfunction is T3 thyrotoxicosis, associated with a decrease in serum thyroid stimulating hormone (TSH), increased T3 level, normal T4, normal free T4, and normal to increase in vitro Uptake results.[7-11] T3 levels are affected by conditions which affect TBG concentration.[12-14] Slightly elevated T3 levels may occur in pregnancy or during estrogen therapy, while depressed levels may occur during severe illness, renal failure, myocardial infarction, alcoholism, inadequate nutritional intake, and during therapy with some medications such as dopamine, glucocorticoids, methimazone, propranolol, propylthiouracil, and salicylates.[6,15,16] Numerous conditions unrelated to thyroid disease may cause abnormal T3 values.[5,17-20] Consequently, total T3 values should not be used on their own in establishing the thyroid status of an individual. The level of serum T4, TSH and other clinical findings must be considered as well.
- 1.O'Neil MJ, editor. The Merck Index. 13th ed. Whitehouse Station, NJ: Merck & Co., Inc., 2001;987-988.
- 2.Ekins RP. Methods for the measurement of free thyroid hormones. In: Free Thyroid Hormones: Proceedings of the International Symposium Held in Venice, December 1978. Amsterdam: Excerpta Medica; 1979:72-92.
- 3. Robbins J, Rall JE. The iodine-containing hormones. In: Gray CH, James VHT, eds. Hormones in Blood. Vol 1. 3rd ed. London: Academic Press, 1979;632-667.
- 4.Demers LM, Spencer CA, eds. Laboratory medicine practice guidelines: laboratory support for the diagnosis and monitoring of thyroid disease. Thyroid. 2003;13:3-126.
- 5.Hollander CS, Shenkman L. Radioimmunoassay for triiodothyronine and thyroxine. In; Rothfeld B, editor. Nuclear medicine in vitro. Philadelphia: Lippincott, 1974;136-49.
- 6.Kaplan MM, Larsen PR, Crantz FR, Dzau VJ, Rossing TH, Haddow JE. Prevalence of abnormal thyroid function test results in patients with acute medical
- 7. Larsen PR. Triiodothyronine: Review of Recent Studies of Its Physiology and Pathophysiology in Man. Metabolism. 1972;21:1073-1092.
- 8. Klee GG. Clinical usage recommendations and analytical performance goals for total and free triiodothyronine measurements. Clin Chem. 1996;42:155-15
- 9. Ivy HK, Wahner HW, Gorman CA. "Triiodothyronine (T3) toxicosis": its role in Graves' disease. Arch Intern Med. 1971;128:529-534.
- 10. Hollander CS, Mitsuma T, Nihei N, Shenkman L, Burday SZ, Blum M. Clinical and laboratory observations in cases of triiodothyronine toxicosis confirmed by radioimmunoassay. Lancet. 1972;1:609-611.
- 11.Sterling K, Refetoff S, Selenkow HA. T3 thyrotoxicosis: thyrotoxicosis due to elevated serum triiodothyronine levels. JAMA. 1970;213:571-575.
- 12.Kaplan MM, Larsen PR, Crantz FR, Dzau VJ, Rossing TH, Haddow JE. Prevalence of abnormal thyroid function test results in patients with acute medical illnesses. Am J Med. 1982;72:9-16.
- 13.Bermudez F, Surks MI, Oppenheimer JH. High incidence of decreased serum triiodothyronine concentration in patients with nonthyroid disease. J Clin Endocrinol Metab. 1975;41:27-40.
- 14. Oppenheimer JH. Thyroid function tests in nonthyroidal disease. J Chronic Dis. 1982;35:697-701.
- 15.Abuid J, Larsen PR. Triiodothyronine and thyroxine in hyperthyrodism: comparison of the acute changes during therapy with antithyroid agents. J Clin Invest. 1974;54:201-208.
- 16.Felig P, Frohman LA, eds. Endocrinology & Metabolism. 4th ed. New York: McGraw-Hill, Inc., 2001:270-311.
- 17.Bates HM. Clin Lab Prod 1974;3:16.
- 18.Utiger RD. Serum triiodothyronine in man. Annu Rev Med 1974;2:289-302.
- 19. Larson PR. Triiodothyronine: review of recent studies of its physiology and pathophysiology in man. Metabolism 1972;21:1073-92.
- 20. Oppenheimer JH. Role of plasma proteins in the binding, distribution and metabolism of the thyroid hormones. N Engl J Med 1968;278:1153-62.
|Detection Range||0.77~7.7nmol/L (0.5~5 ng/mL)|
|Sample Type||Serum, Plasma|