Triiodothyronine T3

Test Details

Synonyms

• T3, Total

Use

Thyroid function which is particularly useful in the diagnosis of T3 thyrotoxicosis, in which T3 is increased and T4 is within normal limits. T3 toxicosis is occasionally found in Graves' disease. It occurs with a single toxic nodule, multinodular thyrotoxicosis, and following treatment with T3 (Cytomel®).2 It is increased in and occasionally helpful for confirmation of diagnosis of conventional hyperthyroidism, in which commonly both T3 and T4 levels are increased. T3 is needed in patients with clinical evidence for hyperthyroidism, in whom the usual thyroid profile is normal or borderline. Reported to be normal to slightly increased with familial dysalbuminemic hyperthyroxinemia. Recommended for patients with supraventricular tachycardia, for patients with fatigue and weight loss not otherwise explained, or for those with proximal myopathy and in whom T4 levels are not elevated.3