Thyroiditis INDEX

TSH, T3, T, T3-resin uptake, free thyroxin index), but careful attention to early signs and symptoms of hypofunction (e.g., weight gain, cold intolerance, hair loss) may be more productive. Thyroid-stimulating hormone is sensitive to early thyroid changes and, if elevated, should prompt treatment with thyroid supplements to avoid goiter or hypothyroidism. 

US Department of Health and Human Services Potassium iodide as a thyroid blocking agent in radiation emergencies. December 2001 (http //www.fda.gov/cder/guidance/index.htm). 

The etiology and pathogenesis of hypothyroidism are outlined in Table 38-5. Hypothyroidism can occur with or without thyroid enlargement (goiter). The laboratory diagnosis of hypothyroidism in the adult is easily made by the combination of a low free thyroxine (or low free thyroxine index) and elevated serum TSH (Table 38-2). 

Hypothyroid women frequently have anovulatory cycles and are therefore relatively infertile until restoration of the euthyroid state. This has led to the widespread use of thyroid hormone for infertility, although there is no evidence for its usefulness in infertile euthyroid patients. In a pregnant hypothyroid patient receiving thyroxine, it is extremely important that the daily dose of thyroxine be adequate because early development of the fetal brain depends on maternal thyroxine. In many hypothyroid patients, a modest increase in the thyroxine dose (about 20-30%) is required to normalize the serum TSH level during pregnancy. Because of the elevated maternal TBG, the free thyroxine index (FT4I) or free thyroxine (FT4) and TSH (Table 38-2) must be used to monitor maternal thyroxine dosages. 

Her body mass index (BMI) was 31.5 kg/m2, which is more than 97% of that for her age. Her thyroid was not enlarged, the cardiac examination was normal, and the lung examination was normal without any wheezing (a high-pitched, flutelike noise with expiration often seen with asthma). She had a dark, thick skin rash in the folds on her neck called acanthosis nigricans. 

Lithium salts have a narrow therapeutic index. Lithium levels should be monitored every 3 months. The long-term use of lithium is associated with thyroid disorders and mild cognitive and memory impairment. Thyroid and renal functions should be checked every 6-12 months,... 

The THBR is derived from a version of the T3 or T4 uptake test. Uptake tests are used to estimate the number of unoccupied (unsaturated) thyroid hormone bindhig sites on serum proteins. This information is important because variations in total thyroid hormone concentrations in blood, as discussed previously, have resulted from changes in binding protein concentrations. Values obtained by uptake methods are expressed as a THBR, which is directly proportional to the free hormone fraction (within limits). Measurement of THBR, in conjunction with a total hormone concentration, is a clinically useful indirect method for calculating the FT4 (or FT3) index. The index approach is particularly useful in patients with nonthyroidal illness in whom FT4 immunoassay methodologies are unreliable. Specifically, TT4 measurement is more diagnostically useful in such patients provided that values are interpreted in accord with the severity of illness in the patient that is indirectly reflected by abnormalities in THBR. 

Calculation of Free T and Tg Indexes The THBR assay is not designed to be used as an independent and isolated test for thyroid disease. It is useful only when combined with a measurement of total T4 (or Tg) concentration to calculate an FT4 or FT3 index. 

Faix JC, Rosen HN, Valazquez FR. Indirect estimation of thyroid hormone-binding proteins to calculate free thyroxine index comparison of iionisotopic methods that use labeled thyroxine ( T-Uptake ). Cfin Chem 1995 41 41-7. 

McCormack G> Faix J. Evaluation of chemiluminescent enzyme immunoassay for thyroid binding globulin (TBG) and comparison of T4/TBG ratio with free thyroxin index. Clin Chem 1990 36 1149. 

Eales, J.G., S.B. Brown, D.G. Cyr, B.A. Adams and K.R. Finnson. Deiodination as an index of chemical disruption of thyroid hormone homeostasis and thyroidal status in fish. In Environmental Toxicology and Risk Assessment Standardization of Biomarkers for Endocrine Disruption and Environmental Assessment Eighth Volume, ASTM STP 1364, edited by D.S. Henshel, M.C. Black and M.C. Harrass, West Conshohocken, PA, American Society for Testing and Materials, pp. 136-164, 1999. 

After treatment is initiated, patients should be examined and thyroid function tests (serum-free thyroxine index and total triiodothyronine concentrations) measured every 2 to 4 months. Once euthyroidism is established, follow-up every 4 to 6 months is reasonable. 

Cardiovascular Effects Thyroid hormones directly and indirectly influence cardiac function, and cardiovascular manifestations are prominent clinical consequences of thyroid disease. In hyperthyroidism, there is tachycardia, increased stroke volume, increased cardiac index, cardiac hypertrophy, decreased peripheral vascular resistance, and increased pulse pressure. In hypothyroidism, there is bradycardia, decreased cardiac index, pericardial effusion, increased peripheral vascular resistance, decreased pulse pressure, and elevation of mean arterial pressure. 

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