SERUM THYROTROPIN AND THYROID-HORMONE LEVELS IN ELDERLY AND MIDDLE-AGED EUTHYROID PERSONS

Objective: To determine whether serum thyrotropin (TSH) levels are altered in euthyroid older persons compared with middle-aged adults. Design: Serum TSH and thyroid hormone levels were measured in a large group of older persons (>70 years old, n = 216) and their middle-aged offspring (40-60 years old, n = 211) after excluding those with clinical or historical evidence of thyroid disease or abnormal thyroid function. Measurements: Serum TSH, thyroxine (T4), free T4 index, estimated free T4, triiodothyronine (T3), estimated free T3, and ferritin levels were measured on the Abbott IMx instrument. Peroxidase and thyroglobulin antibodies were measured by radioimmunoassay using Kronus kits. Main Results: Overall, serum TSH showed a log-normal distribution. The geometric mean TSH (mU/L) and 95% confidence limits in the older persons, 1.24 (0.29-5.4), did not differ significantly from that in the middle-aged, 1.45 (0.54-3.9). The mean TSH in the 264 women, 1.37 (0.34-5.5), was similar to that of the 163 men, 1.30 (0.48-3.5). The mean TSH in older women, 1.21 (0.22-6.6), was slightly but significantly lower than that in middle-aged women, 1.52 (0.55-4.2). However, when euthyroid women with positive antibodies were excluded, this difference was not significant. Four of the 123 older women had TSH <0.1 mU/L, but none of the men or middle-aged women had a suppressed serum TSH. The mean TSH in older men, 1.28 (0.43-3.8), was similar to that in middle-aged men, 1.32 (0.55-3.2). Free T4 was slightly higher in older women than middle-aged women. There were no significant correlations between TSH and any thyroid hormone level. Serum ferritin, measured as a potential marker for the action of thyroid hormone, did not correlate with any measure of thyroid function. At least one antibody level was >10 U/mL in 14.6% of older women, 15.6% of middle-aged women, 4.3% of older men, and no middle-aged men. When those with milder elevations of antibody levels were included (at least one level >1 U/mL), the prevalence was 32% of older women, 43.3% of middle-aged women, 15% of older men, and 11.4% of middle-aged men. Conclusions: Euthyroid older persons have about the same levels of serum TSH as younger ones, although older euthyroid women have a slightly lower serum TSH than middle-aged women. We recommend that the normal range of serum TSH in the elderly be considered to be the same as that in healthy middle-aged subjects.