Measurement of total thyroxine is mainly used to monitor the treatment of thyroid diseases with synthetic hormones and to monitor the treatment of hyperthyroidism with thiouracil and other antithyroid drugs.
Thyroxine (T4) is a hormone produced in the thyroid gland by iodine and thyroglobulin in a multi-step process. The production is made in response to the thyroid-stimulating hormone (TSH) stimulus in the thyroid gland. Thyroxine is the major hormone synthesized by the gland and is the hormone from which triiodothyronine (T3) is derived. When released from the thyroid gland, almost all (99.96%) of T4 binds to proteins (thyroxine-binding globulin, thyroxine-binding pre-albumin, and albumin). The remainder of T4 (0.04%) is called free thyroxine (FT4) and is the only part of the hormone that is biologically active. Biologically active free thyroxine stimulates the basic metabolic rate, including the utilization of carbohydrates and lipids, protein synthesis, bone calcium release, and vitamin metabolism. In infants, thyroxine plays an important role in the development of the central nervous system and in the development. Circulating levels of thyroxine affect the release of TSH and hypothalamic thyrotropin-releasing hormone (TRH) through a negative feedback mechanism.
Possible Interpretations of Pathological Values
- Increase: Acute intermittent porphyria, primary biliary cirrhosis, a relative excess of thyroxine-binding globulin, excessive iodine intake, familial dysalbuminemic hyperthyroxinemia, toxic multinodular goiter, Graves’ disease, hyperthyroidism, liver disease, lymphoma, in newborn infants, obesity, pregnancy, acute psychiatric disorder, acute thyroiditis, thyrotoxicosis. Medications: amiodarone, amphetamines, Betadine, clofibrate, dextrothyroxine, estrogens, furosemide, 5-fluorouracil, halothane, heparin, heroin, iodine contrast media, iodothiouracil, iopanoic acid, levodopa, methadone, oral contraceptives, perphenazine, phenylbutazone, progesterone, beta-blockers, thyroid extract, thyroid-releasing hormone, thyroid hormone, thyroxine, clioquinol
- Decrease: Acromegaly, cirrhosis, cretinism, eclampsia, vigorous exercise, genetic deficiency of thyroxine-binding globuline, goiter, thyroiditis Hashimoto (chronic thyroiditis), hypoproteinaemia, hypothyroidism (primary, secondary), severe iodine deficiency, chronic liver disease, malnutrition, myxedema, nephrosis, nephrotic syndrome, malabsorption, pan-hypoputitarism, post-operative (due to stress), preeclampsia, radioactive iodine therapy, Sheehan's syndrome, Simmonds's disease, subacute thyroiditis, thyroidectomy, thyroid gland agenesis, pituitary tumor. Medications: Corticosteroids, adrenocorticotrophic hormone, amiodarone (rare), androgens, anabolic steroids, antithyroid drugs, asparaginase, barbiturates, carbamazepine, chlorpromazine, corticotropin, cortisone (long term use), danazol, diphenylhydantoin, ethionamide, fenclofenac, furosemide (high doses); gold salts, iodide, isoniazid (long-term use), isotretinoin, lithium carbonate, L-triiodothyronine, methimazole, oxyphenbutazone, penicillin, phenobarbital, phenytoin, prednisone, prednisone gels, reserpine, rifampicin, salicylates, somatropin, sulfonamides, thiocyanates.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.