Use of 99 Tc m for the routine assessment of thyroid function.

(99)Tc(m)-pertechnetate is concentrated in the thyroid in the same way as iodide but it does not become organically bound. The uptake of (99)Tc(m) is a measure of the thyroid trap, and this measurement is satisfactory as a routine test in the diagnosis of thyrotoxicosis. The reproducibility of the method is such that suppression tests can be carried out when necessary even when uptake is within the normal range of 0.4-3%. (99)Tc(m) gives a low radiation dose to the thyroid and has certain other advantages over radioactive isotopes of iodine for early thyroid uptake measurements. It is particularly suitable when serial tests of thyroid function are required during treatment with an antithyroid drug.