[Thyroid suppression test].

A test in which thyroid function is suppressed was evaluated in regard to its ability to confirm the diagnosis of hyperthyroidism in borderline cases. An effort was made to establish a standard technique by determining the required duration of administration of tri-iodothyronine. Twenty-seven normal controls received tri-iodothyronine (T(3)) for a 10-day period, and 24-hour I(131) uptake was determined after three, six and 10 days. Twenty-two normal controls were similarly studied after four days of T(3) treatment. Twenty-one patients with an elevated I(131) uptake without goitre or toxicity, 10 with non-toxic goitre and 11 with toxic goitre were also studied. The T(3) suppression test was found to be particularly useful in distinguishing toxic goitre from euthyroid patients with an elevated I(131) uptake. Four days of suppression were found to be sufficient for purposes of evaluation in a large majority of cases.