Thyroid function in a healthy elderly population: implications for clinical evaluation.

Evaluation of thyroid function in elderly people is complex and has generated some controversy about what is normal. This study analyzed thyroid function assays in an identified healthy elderly population of 216 subjects. Thyroxine, free thyroxine, triiodothyronine, T3 uptake, "supersensitive" thyrotropin, and thyroid antibody titers were performed. Histories of treatment for thyroid conditions were present in 13.9% (n = 30) of the population, and test results for an additional 4.3% (n = 8) revealed some hypothyroidism. These subjects were excluded from statistical analysis. Test results revealed significant differences from younger controls as well as skewed distributions for T4, FT4, and TSH. There were no significant correlations with increasing age or gender within the elderly population. 11.8% (n = 21) of the population exhibited elevated TSF levels with normal T4 values, and 23.0% (n = 41) exhibited a titer of one or both thyroid antibodies. Current reference ranges for thyroid tests are broad enough to include the range of values seen in the healthy elderly, but some cautions are discussed.