Technetium-99 m in the diagnosis of thyrotoxicosis

The thyroid uptake at 20 minutes of intravenously administered Technetium-99(m) ((99m)Tc) was measured in 117 patients with a standard scintillation counter. Patients were divided into three groups on the basis of clinical assessment, four-hour (131)I uptake, triiodothyronine (T-3) resin uptake, and protein-bound iodine measurements.In 31 patients with no evidence of thyroid disease the mean (99m) Tc uptake was 1.8% +/-S.D. 1.1%. In 32 patients with thyroid enlargement who were euthyroid the mean uptake was 2.5% +/-S.D. 2.2%. In 54 thyrotoxic patients the mean uptake was 17.7% with a range of 4.1 to 44%, all cases having an uptake above the upper limit of normal (4.0%). These results agree closely with reported uptake studies using scanning techniques. In seven patients the extrathyroidal neck activity was measured by using a scanner, and the mean was 6.3% of the extrathyroidal total body radioactivity comparing favourably with an assumed 6% used in our calculations.We have shown that the measurement of the thyroid uptake of (99m)Tc with a scintillation counter is of value, and that it is not necessary to use scanning techniques in the diagnosis of thyrotoxicosis. Advantages of (99m) Tc are minimal radiation, reduction in patient and laboratory time, and low cost.