Unique alterations of thyroid hormone indices in the acquired immunodeficiency syndrome (AIDS)

Article Abstract:

Both thyroid and nonthyroid diseases are known to alter amounts of circulating thyroid hormones. When illnesses that do not originate in the thyroid gland progress, the level of triiodothyronine (T3) falls, reverse T3 (rT3) rises and thyroxine T4 and thyrotropin (TSH) usually remain close to normal. However, some critically ill patients can also have decreased T4. The chance of death increases as T4 levels decrease, and therefore T4 indices can be used to predict the outcome of critically ill patients. This study was conducted to see if similar thyroid hormone determinants could be used to predict the progression and outcome of patients infected with the human immunodeficiency virus (HIV). Patients at different stages of AIDS (acquired immunodeficiency syndrome) were evaluated for thyroid hormone levels. There were 26 hospitalized patients with pneumocystis carinii (a common AIDS-related lung infection), 10 outpatients with AIDS, 10 outpatients with AIDS-related complex (a pre-AIDS stage that produces milder symptoms) and 10 outpatients with HIV-positive blood. The seven nonsurvivors of P. carinii had lower T3 (0.56 nanomoles/liter) than the 19 survivors (1.3 nmol/L). The rT3 was 0.21 nmol/L in patients with AIDS-related complex and 0.17 nmol/L in AIDS outpatients. The rT3 level became more normal when patients reached the point that they needed to be hospitalized. The protein essential for thyroxine to bind to carrier proteins decreased as the HIV infections intensified. Those who died tended to have normal T3, rT3 and thyroxine-binding proteins. As HIV infections progress, rT3 decreases and thyroxine-binding globulins increase. Normal T3 levels are thought to be responsible for the significant weight loss in AIDS patients. The cause of thyroid hormone changes is unclear. Low T3 can provide useful information on the clinical course of HIV-infected patients. Thyroid hormone determinants may be used to help make decisions regarding therapy. (Consumer Summary produced by Reliance Medical Information, Inc.)

Prognosis, AIDS (Disease), Triiodothyronine

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American Thyroid Association guidelines for use of laboratory test in thyroid disorders

Article Abstract:

In recent years a large number of new laboratory tests for the detection of thyroid disorders have become available, which may cause some confusion. To help the clinician select the most efficient and specific diagnostic test, the American Thyroid Association has created guidelines to simplify patient evaluation; these are outlined in this article. Testing of the general population is not recommended because of the relatively low incidence of undiagnosed thyroid disorder. Specific targets for screening include those with a family history of thyroid disease, elderly patients, and women who have recently given birth. Two principal laboratory tests are: the estimation of free thyroxine, a hormone produced by the thyroid gland; and a sensitive thyrotropin (a thyroid-stimulating hormone produced in the pituitary gland) assay test. Hypothyroidism (deficient secretion of the thyroid hormones) hyperthyroidism (excessive secretion of thyroid hormones) and the optimal treatments for both conditions are discussed, as are the effects of several frequently prescribed drugs on thyroid function. Pregnancy is also often complicated by thyroid abnormalities. Hypothyroidism is indicated by a decrease in serum free thyroxine and an increase serum thyrotropin. Thyrotoxicosis is indicated by an increase in free thyroxin, along with a reduced serum-sensitive thyrotropin level. Patients that are very ill with other conditions may show elevated serum free thyroxine with normal serum thyrotropin, which is not necessarily symptomatic of thyroid disease. Some drug treatments may result in thyroid symptoms and unusual thyroid disorders typically result in confusing laboratory results. (Consumer Summary produced by Reliance Medical Information, Inc.)

Analysis, Testing, Thyroid diseases, Thyrotropin, Thyroid gland function tests, Thyroid function tests

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Normal serum free thyroid hormone concentrations in patients treated with phenytoin or carbamazepine: a paradox resolved

Article Abstract:

The finding of decreased thyroid hormone levels in people taking anticonvulsants appears to be an artifact of the test used to measure the hormone levels. Researchers took blood samples from 9 people taking phenytoin and 10 people taking carbamazepine. All 19 had no history of thyroid disease. Adding therapeutic concentrations of the drugs to the blood samples caused total T4 thyroid hormone to drop significantly, but free T4 hormone increased substantially when measured by an assay that uses undiluted blood. This increase in free T4 was not seen when the hormone was measured using an assay that dilutes the blood. In fact, free T4 levels dropped. These drugs displace T4 from T4-binding proteins. This would tend to raise free T4 levels. However, when blood samples are diluted, the drug concentration drops substantially and no longer displaces T4. Physicians should monitor TSH levels in these patients, since TSH levels are usually normal.

Physiological aspects, Anticonvulsants

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