The thyroid

Thyroid function has been extensively studied in the elderly. Early studies reported significant alterations in thyroid hormone and thyrotropin (TSH) levels, as well as blunted TSH responses to exogenous thyrotropin-releasing hormone (TRH) in older subjects. However, more recent studies revealed that most of these alterations are due to the effects of illness and medications on thyroid hormone levels. Acute or chronic non-thyroidal illness decreases serum tri-iodothyronine (T3) levels, and more severe illness also decreases serum thyroxine (T4) levels. Serum TSH levels are usually normal, but decrease as the illness becomes more severe, and TSH responses to TRH are blunted. During recovery from acute illness, serum TSH and T4 rise in parallel, and TSH may temporarily exceed the normal range. Glucocorticoids and dopamine reduce TSH levels, and amiodarone and propranolol block conversion of T4 to T3, thus elevating serum T4 and lowering T3 levels. For these reasons, interpretation of thyroid function tests in the elderly must include an assessment of possible effects of non-thyroidal illness or medications.