Serum thyrotropin

Lithium blocks the release of thyroxine (T4) and triiodothyronine (T3) mediated by thyrotropin (Kleiner et ah, 1999). This results in a decrease in circulating T4 and T3 concentrations and a feedback increase in serum thyrotropin concentration. It also inhibits thyrotropin-stimulated adenylate cyclase activity (Kleiner et ah, 1999). Lithium has varying effects on carbohydrate metabolism. Increased and decreased glucose tolerance and decreased sensitivity to insulin have been observed (Van derVelde Gordon, 1969). In animals, lithium decreases hepatic cholesterol and fatty acid synthesis. 

A 61-year-old woman with hypothyroidism had celiac disease and a history of bowel resection for pancreatic cancer, was euthyroid taking thyroxine 175-188 micro-grams/day (74). However, when she simultaneously took calcium carbonate (1250 mg/day) she had a raised serum thyrotropin (TSH) concentration of 41 mU/1. Delaying calcium carbonate ingestion by 4 hours returned her serum TSH concentration to high normal (5.7 mU/1) within a month. 

Sawin CT, Geller A, Wolf PA, Belanger AJ, Baker E, Bacharach P, Wilson PW, Benjamin EJ, D Agostino RB. Low serum thyrotropin concentrations as a risk factor for atrial fibrillation in older persons. N Engl J Med 1994 331(19) 1249-52. 

McCowen KC, Garber JR, Spark R. Elevated serum thyrotropin in thyroxine-treated patients with hypothyroidism given sertraline. N Engl J Med 1997 337(14) 1010-1. 

Interleukin-6 reduced serum thyrotropin and thyroid hormone concentrations and increased LH concentrations (SEDA-20, 336). 

Peak serum thyrotropin levels occur 20-30 seconds after intravenous TRH injection in healthy individuals. In hyperthyroidism, the serum thyrotropin level is suppressed. In primary hypothyroidism, thyrotropin levels are high and the thyrotropin response to TRH may be accentuated. In secondary (pituitary) hypothyroidism, serum thyrotropin levels are "inappropriately" normal or low (using a sensitive TSH assay) TSH often fails to rise after TRH administration. In tertiary (hypothalamic) hypothyroidism, the baseline serum thyrotropin level may be normal or low and the thyrotropin response to TRH may be normal or blunted. 

TRH testing (see above) is now rarely used to diagnose hyperthyroidism or hypothyroidism, having been supplanted by sensitive assays for serum thyrotropin (see below). 

Waritz RS, Steinberg M, Kinoshita FK, Kelly CM, Richter WR (1996) Thyroid function and thyroid tumors in toxaphene-treated rats. Regul Toxicol Pharmacol 24 184-192 Weeke J (1973) Circadian variation of the serum thyrotropin level in normal subjects. Scand J Clin Lab Invest 32 337... 

Spencer CA, Takeucho M, Kazarosyan M. Current status and performance goals for serum thyrotropin (TSH) assays. Clin Chem 1996 42 140-5. 

Stockigt JR. Chapter 18 Serum thyrotropin and thyroid hormone measurements and assessment of thyroid hormone transport. In Braverman LE, Utiger RD, eds. Werner and Ingbar s the thyroid. 7th ed. Philadelphia Lippincott-Raven, 1996 377-96. 

J. Lekakis, C. Papamichael, M. Alevizaki, G. Piperingos, P. Marafelia, J. Mantzos, S. Stamatelopoulos, D. A. Koutras, Flow-mediated, endothelium-dependent vasodilation is impaired in subjects with hypothyroidism, borderline hypothyroidism, and high-normal serum thyrotropin (TSH) values, Thyroid 7, 411-4 (1997). 

We will analyze those thyroid cancers that were shown to have undergone changes in their incidence after the implementation of iodine prophylaxis in different endemic goiter areas, probably through the effect of dietary iodine in relation to serum thyrotropin (TSH) levels and increase of thyroiditis, as well as in relation to the standard of medical care. We will also focus on the effect of salt iodization... 

Figure 63.3 The figure shows the evolution of maternal thyroidal funotion. TSH, serum thyrotropin. fT4, serum free thyroxine. NSD, no signifioant differenoes.

The figure shows that a normal General Cognitive Index requires adequate maternal iodine nutrition conditions and a thyroid function. CGI, General Cognitive Index. UIE, urine iodine excretion. TSH, serum thyrotropin. 

Figure 77.1 Relationship between thyroid uptake (a) or nonhormonal iodine levels (b) and changes in serum thyrotropin (TSH) oompared with the initial levels after iodine restriotion. a/b, TSH after iodine restriction/TSH before iodine restriotion. The o uptake values showed a signifioant inverse correlation with aTSH/bTSH values (P = 0.001, r = 0.600, a). Serum nonhormonal iodine levels were inversely oorrelated with aTSH/bTSH values, but the correlation was not statistically significant (r = 0.355, 0.05 < P < 0.1, b). TSH, thyroid-stimulating hormone.

Figure 106.1 Evaluation of patients with abnormal serum thyrotropin (TSH) oonoentrations. Schematic aigorithm for the evaiuation of a patient with abnormal thyrotropin (TSH) with an indication of the most oommon diagnoses in the absence of nonthyroidai iiinesses and drugs affecting thyroid hormone concentrations. Abbreviations t, high low n, normal FT4, free thyroxine FT3, free triiodothyronine L-T4, levothyroxine.

Table 106.3 Causes of increased serum thyrotropin concentrations...

The prevalence of subclinical hypothyroidism (SCH), defined as serum thyrotropin (TSH) concentration above the upper limit of the reference range with normal free thyroxine (FT4), in women of child-bearing age may be as high as 5% (Canaris et al., 2000 Hollowell et al., 2002). Of these, approximately 2—5% per year will progress to overt hypothyroidism (OH), defined as low serum FT4 with elevated serum TSH concentration. When iodine nutrition status is adequate, the most frequent cause of hypothyrod is thyroid autoimmunity (Hashimoto s thyroiditis) and, in this respect, if we take into account women with thyroid autoimmunity and normal thyroid function who could become... 

Serum Thyrotropin Levels Increased as Levels of Iodine Intake Rose... 

The Upper and Lower Limits of Serum Thyrotropin within the Safety Range... 

The safety range of serum thyrotropin has been the focus of endocrinologists all over the world. People... 

Figure 125.6 The cumulative incidence of abnormal levels of serum thyrotropin at 5 years among 2727 subjects who had normal levels of serum thyrotropin at baseline. The relationship between the baseline thyrotropin levels in 1999 and the cumulative incidence in 2004 of supranormal serum thyrotropin levels (above 4.8mlU/l) (panel a) or subnormal serum thyrotropin levels (below 0.3mlU/l) (panel b) is shown. A serum thyrotropin level above 1.9mlU/l (filled circle in panel a) was associated with an increased incidence of a supranormal thyrotropin level a drop in serum thyrotropin level below 1. OmIU/l (filled circle in panel b) was associated with an increased incidence of a subnormal thyrotropin level.

The level of serum thyrotropin increased as the levels of iodine intake rose. 

Patients with hypothyroidism and organic depression may need both levothyroxine and antidepressant drug therapy, in ievothyroxine-treated patients with hypothyroidism who were treated with sertraiine, there was an eievated serum thyrotropin concentration, indicative of a decrease in the efficacy of ievothyroxine. What is the possible mechanism of interaction between the two drugs ... 

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