Laboratory examination of the thyroid. II. In vivo tests

In vivo tests of thyroid function are indicated if results of in vitro tests are inconclusive, equivocal, or require confirmation. These tests are based on the thyroid's ability to concentrate iodine and involve administration of a radioisotope and external detection. The radioactive iodine uptake test involves measuring thyroid activity, in some cases before and after thyroid stimulation or suppression. Scanning gives a picture of the gland itself. (U.S.)