Clinical follow-up with repeat measurement of thyroid-stimulating hormone (TSH) and free thyroxine (T4) is the most appropriate management for this patient. In persons over 80 years of age, the serum TSH level may be mildly elevated above the typical reference range for younger adults. The upper limit of the normal range in this elderly population without thyroid dysfunction may be as high as 8.0 µU/mL (8.0 mU/L). Since this patient's TSH level is 6.4 µU/mL (6.4 mU/L), his clinical symptoms are nonspecific, and his physical examination is normal, additional evaluation or treatment is not indicated at this time. However, his clinical symptoms should be monitored, and his serum TSH and free T4 levels should be measured repeatedly several times over a period of months to ensure that the TSH value is not part of a trend to the development of overt thyroid dysfunction.
Because this patient's serum free T4 level is normal and a diagnosis of hypothyroidism has not been established, he does not require levothyroxine therapy.
Measurement of the serum total triiodothyronine (T3) level is not typically helpful in diagnosing hypothyroidism because total T3 levels may remain within the normal range well into the evolution of hypothyroidism. However, total T3 levels are useful in evaluating patients with possible hyperthyroidism because the value may be elevated out of proportion to the T4 level, and failure to recognize an elevated T3 value may underestimate the degree of hyperthyroidism present.
Total T4 measures both the bound and unbound thyroid hormone fractions, whereas the free T4 reflects the unbound portion of hormone, and may more accurately reflect available hormone levels in patients who may have an abnormality in protein metabolism (such as liver or kidney disease). However, measurement of total T4 in addition to free T4 would not provide additional diagnostic information in this patient.