Reevaluation of patients on thyroxine therapy.

A 21-day withdrawal test was utilized at four primary care practice sites to reevaluate individuals on thyroxine therapy. Utilizing elevated thyroid stimulating hormone (TSH) concentrations as the standard for diagnosing hypothyroidism, 22 of 37 patients previously on thyroxine were found to be euthyroid. Of the 15 hypothyroid individuals identified, 13 had elevated serum TSH 21 days after withdrawal of thyroxine. Two individuals who had serum TSH concentrations in the normal range at 21 days became symptomatic at five and eight weeks, respectively, and were found to have elevated serum TSH. Several factors may account for the high percentage of euthyroid individuals being treated with thyroid medication. These include unreliability of symptoms as a basis for diagnosis of hypothyroidism, laboratory tests that are often difficult to interpret, the commonly held misconception that all forms of primary hypothyroidism are irreversible, the routine use of thyroxine by many surgeons after subtotal thyroidectomy, and the use of thyroxine to suppress diffuse or nodular goiter.