Thyroid function tests in ageing and their relation to associated nonthyroidal disease.
Thyroid function tests of 179 euthyroid geriatric inpatients (83 +/- 6 yr) unaffected by acute diseases or malnutrition were investigated and compared with those of 76 ambulatory healthy younger subjects (42 +/- 13 yr). Elderly population was divided in three groups, respectively: group G I (n = 37, 65-78 yr), group G II (n = 64, 79-85 yr) and group G III (n = 78, over 85 yr). Severity-of-illness index of the patients was evaluated at entry in the study protocol. While total thyroxine (TT4), free triiodothyronine (FT3) and TSH levels remained unchanged, circulating total triiodothyronine (TT3) was significantly lower (113 +/- 32 vs 150 +/- 31 ng/dl, p less than 0.05) and free thyroxine (FT4) was significantly higher (12.4 +/- 2.7 vs 10.3 +/- 2.3 pg/ml, p less than 0.05) in aged people. Furthermore, TT3 decreased significantly from 130 +/- 36 in G I to 110 +/- 33 in G II and to 108 +/- 25 in G III (p less than 0.01), and FT4 increased progressively although not significantly in the same groups. A close correlation was found between TT3 and severity index in male observations only (r = -0.43, p less than 0.01), as well as between FT4 and severity index in both sexes (r = 0.51, p less than 0.001 for men, r = 0.21, p less than 0.01 for women). These data suggest that thyroid function tests have to be cautiously interpreted in a geriatric population, particularly in relation to the severity of the clinical state, and reference values should be determined for TT3 and FT4 in the ageing process.