99mTechnetium - retention.

ABSTRACT

99mTc-retention is a new index for thyroid function studies. The residual 99mTcO4 content in the thyroid was determined 1 hour after KCIO4 administration. The ratio between the residual and uptake by oral administration, called "99mTechnetium retention," in the hyperthyroid is less than 19.5%. A comparision of diagnostic accuracy between 99mTechnetium retention and other techniques, 99mTechnetium-uptake, RIA serum T3 and T4 was carried out in 200 patients, This yielded overall sensitivity of 93.0%, 91.2%, 82.7%; specificity of 99.3%, 89.1%, 99.2% and 100.0% and accuracy of 97.4%, 89.7%, 94.5%, and 92.3% respectivity. This index is very effective for identifying (1) hyperthyroid and iodine deficiency goiter witout suppression test, (2) relapse and remission of Grave's disease after medical therapy. However such index is not applicable to iodine thyrotoxicosis, thyrotoxicosis factitia, ectopic thyroid production and hyperthyroiditis. Perchlorate (CIO4) ions are not only a competitive inhibitor of TcO4 from the gland. Therefore this technique exposes the least radiation hazard to the gland.