Euthyroid "thyroxine toxicosis".

A survey was made of thyroid function tests on 1,153 patients screened for thyroid disease during a two-year period in a Geriatric Department; 13 percent of the test results fell outside the normal range. Of 88 patients who showed above-normal results, only 12 presented with clinical features of thyrotoxicosis. In 37 patients, the biochemical findings indicated euthyroid "thyroxine toxicosis"; high values were found for serum thyroxine (T4) and the free thyroxine index (FT4I) but there were no clinical signs or symptoms of thyrotoxicosis; the values reverted to normal within one to three weeks. This pattern was seen also in 7 examples of T4-treated hypothyroidism. (Overall, the test findings indicated 61 cases of hypothyroidism.) The significance of this transient increase in T4 and FT4I values is discussed. The false positive results suggest that, when laboratory findings are not compatible with the clinical signs, the thyroid function tests should be repeated after another two weeks.