Diagnosis of Thyroid Dysfunction-Reply

—To maximize screening sensitivity, we designated 2,267 patients who had an FT 4 I of 141 to 340 (normal, 121 to 360) plus total T 4 levels of 5.5 to 10.4 μg/dL (normal, 4.5 to 11.4 μg/dL) as "highly probable euthyroid." Of these patients, one third were randomly selected for careful study, including their TSH levels. None had thyroid dysfunction. All remaining patient groups were similarly fully studied. Of asymptomatic euthyroid patients, 1% had isolated high TSH levels (7 to 15 μU/mL). Evered et al 1 defined such patients with normal FT 4 Is and some elevation of TSH levels as having "subclinical hypothyroidism," giving six of 22 thyroid medication without symptomatic change. We chose not to treat but to follow up those patients with subclinical hypothyroidism. All our symptomatic hypothyroid patients happened to have a low FT 4 I. We found uncommon "T 3 toxicosis," defined as a syndrome with