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.
ABSTRACT
99mTc-pertechnetate for thyroid function studies is given oral, need not be sterile or pyrogen-free. The patients need be fasting only 3 hours and no food should be ingested for at least two hours following the oral administrations. The optimum time for uptake measurement is 2 hours after dose. The euthyroid range is from 2.5-11.2%. The suppression test can be carried out with 60 microgram of T3 daily for 5 days. A normal uptake response to T3 is a suppression to < 80% of initial uptake. Poor suppression is characteristic of grave’s disease. The comparison between 99mTc-uptake and RIA, serum T4 and T3 in 50 patients results in similar findings in both euthyroidism and hyperthyroidism, except for one subject with heart disease. The uptake and suppression test can give more information about iodine deficiency goiter. Using 131I and 99mTcO4, we compared 240–iodine uptake and 20-technetium uptake in the same subjects. The diagnosis of 33 patients was made on clinical grounds and confirmed by RIA-technique. The indications were the same, but the iodine uptake was more sensitive, for 6 patients with iodine deficiency disease whereas technetium found only 3. The suppression studies, 131I is satisfied in all cases. Technetium is reasonable in hyperthyroidism and iodine deficiency goiter. If 20-uptake is in normal range, some of them are a suppression and some fail to suppress. Because the normal rang of technetium is lower than iodine and the thigh correction for extrathyroid activity is inadequate. In patients with low 99mTc-uptake, the suppression test is not needed neither are there cases of thyrotoxicosis with false low 99mTc-uptake such might occur with early iodine avidity and wash out at 24 hours.