Clinical significance of low serum thyrotropin concentration by chemiluminometric assay in 85-year-old women and men

Article Abstract:

Thyrotropin, also known as thyroid-stimulating hormone (TSH), is produced by the pituitary gland. It stimulates the thyroid gland, causing the release of the two major thyroid hormones, triiodothyronine (T3) and thyroxine (T4). The thyroid hormones exert a negative feedback on the pituitary, suppressing the release of thyrotropin. It is often difficult to diagnose thyroid disorders, especially in the elderly, and the measurement of thyrotropin has been suggested as the sole diagnostic test. However, other illnesses can cause low thyrotropin levels, and it has been shown that many elderly patients with low thyrotropin levels do not have thyroid disease. Accordingly, 35 85-year-old men and women who were found to have low thyrotropin levels were followed for three years. Eighteen were not receiving thyroid hormone treatment, and no cause could be found for their low thyrotropin levels. They did not suffer from hyperthyroidism, in which excess levels of thyroid hormones inhibit the production of thyrotropin. In addition, they did not have abnormalities in thyroxine-binding globulin. Abnormalities in the binding of thyroid hormones to thyroxine-binding globulin would cause more free thyroid hormones in the blood, which would lead to decreased production of thyrotropin by the pituitary. The condition of low thyrotropin levels in patients who have no symptoms of hyperthyroidism has been called 'subclinical hyperthyroidism', but these patients had no evidence of hyperthyroidism during the 1- to 3-year follow-up. It has also been thought that low thyrotropin levels in critically ill patients (especially at night, when thyrotropin normally rises) are a sign of a poor prognosis. But half the patients in this study were still alive at the 3-year follow-up. Thus, low thyrotropin levels in the elderly are not necessarily a sign of hyperthyroidism or impending death. Better diagnostic tests will help to identify elders who are truly hyperthyroid. (Consumer Summary produced by Reliance Medical Information, Inc.)

Aged, Elderly, Physiological aspects, Thyroid hormones

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Thyroid dysfunction in adults over age 55 years; a study in an urban US community

Article Abstract:

The prevalence of impaired thyroid gland function was assessed among 968 healthy individuals over the age of 55 years. Increased levels of thyrotropin, a hormone that activates thyroid gland secretion, were detected in 7.3 percent of subjects and suppressed levels of thyrotropin were found in 2.5 percent of subjects. Testing with the substance protirelin, which activates the release of thyrotropin, produced exaggerated responses in 95 percent of subjects with elevated thyrotropin levels and subnormal responses in 81 percent of subjects with suppressed thyrotropin levels. Impaired function of the thyroid gland, as indicated by abnormalities in levels of thyrotropin and protirelin response, was estimated in 8.9 percent of subjects. Impaired thyroid function was more prevalent among whites, women, and subjects more than 75 years of age. Hypothyroidism, or decreased activity of the thyroid gland, was detected in 6.9 percent of subjects, who had autoantibodies or abnormal immune proteins that bind to tissues and natural factors. However, only 8.5 percent of these subjects had subnormal levels of thyroxine, a hormone released by the thyroid gland. Hyperthyroidism, or increased activity of the thyroid gland, was detected in 2 percent of subjects; 75 percent of these individuals were taking thyroid hormone preparations. These results indicate that impaired thyroid function is prevalent among the elderly, and occurs with sex and racial differences. (Consumer Summary produced by Reliance Medical Information, Inc.)

Thyroid diseases, Thyroxine

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