Low serum triiodothyronine and high serum reverse triiodothyronine in old age: an effect of disease not age.

Serum concentrations of T4, T3, T3, free T4, free T3, and TSH were determined in four groups of adult subjects: group A, 27 healthy young volunteers (aged 18-29 yr); group B, 24 carefully selected healthy elderly subjects (aged 70-90 yr); group C, 41 subjects living at a municipal nursing home for the elderly (aged 70-90 yr); and group D, 35 hospitalized patients (aged 70-90 yr). Identical levels of iodothyronines in serum were found in the young and in the elderly healthy subjects. Moderate and severe disease induced alterations in iodothyronine concentrations in serum comparable to those reported earlier. Serum T3 and free T3 levels were low and serum rT3 levels were high in groups C and D subjects; serum free T4 was elevated in group D, while serum T4 was low. Serum TSH was lower in the healthy elderly subjects than in the young subjects. Serum TSH was higher in the elderly sick subjects (groups C and D) than in the healthy subjects (group B). We conclude that advanced age per se is not accompanied by alterations in free or total serum iodothyronine levels.