Are patients with low serum thyroid stimulating hormone and normal total thyroxine hyperthyroid? Usefulness of 99mTc...

The records of 107 patients who had had thyroid 99m Tc pertechnetate uptake measured, were reviewed. In patients with normal serum thyroxine (T4) and thyroid stimulating hormone (TSH), 35 of 36 with normal uptake and three with high uptake were clinically euthyroid. In patients with high serum T4 and low TSH, seven had normal and 29 had high uptake and all were clinically hyperthyroid. In patients with normal serum T4 and low TSH, 10 of 11 with high uptake were clinically hyperthyroid whereas only two of 18 with normal uptake were. The sensitivity, specificity and positive predictive value of pertechnetate uptake measurements were 83%, 94%, and 91%, respectively. The measurement of pertechnetate uptake is a rapid investigation and may help in the interpretation of patients with undetectable serum TSH found in the presence of normal serum T4.