[Factors influencing serum free T3 and free T4 in elderly euthyroid subjects]

Thyroid function was investigated in 222 elderly euthyroid subjects (79.6 +/- 7.6 years, males 68, females 154). Serum free T3, free T4, and TSH levels were measured by radioimmunoassay. To assess the factors influencing serum free T3 and free T4, we applied multiple regression analysis. 1) Serum free T3 concentrations were directly proportional to both serum albumin levels and hemoglobin levels. Serum free T3 levels were lower in bedridden male subjects and in female subjects with dementia. 2) Serum free T4 concentrations were negatively correlated to serum TSH levels in male. Serum free T4 levels were higher in bedridden female subjects, and increased in proportion to serum albumin concentrations in females. 3) Age had no apparent effect on either serum free T3 or free T4 concentrations.