Wickus, Gary G.

ABSTRACT In four groups of subjects free of thyroid disease, the following determinations were made: serum concentrations of thyroxine (T 4 ), triiodothyronine (T 3 ), reverse T 3 (rT 3 ) and diiodothyronine (T 2 ), and calculated indices of free thyroxine (FT 4 ) and free triiodothyronine (FT 3 ). Group A comprised healthy subjects aged 16–64; Group B, 24 healthy elderly subjects aged 68–95; Group C, 23 elderly patients with mild well‐controlled chronic illnesses, aged 70–85; Group D, 40 nursing home residents aged 66–100. Serum T 4 and T 2 concentrations and the FT 4 index were not affected by age; the rT 3 concentration was slightly but significantly elevated only in Group D patients. Serum T 3 concentration was significantly lower in all groups of elderly subjects and decreased FT 3 index measurements were detected after age 75. It was concluded that old age, without complicating illness, is accompanied only by a decrease in the serum level of T 3 and the FT 3 index; values for other iodothyronines are unchanged. Clinicians should consider the age‐related changes in T 3 and FT 3 values when interpreting thyroid function tests.