Is 99mTechnetium Pertechnetate Thyroid Uptake accurate in Thyrotoxicosis Evaluation?

Abstract BackgroundThis study aimed to evaluate the 99mTc thyroid uptake (TcTU) in terms of (1) normal mean and range, (2) level of uncertainty in thyrotoxic patients and (3) effectiveness of adding radioiodine uptake in patients with uncertain TcTU values.MethodsPatients referred for TcTU test were included and categorized into groups: euthyroid, Graves’ disease, toxic nodular goiter and subacute thyroiditis. Mean and range of TcTU were obtained separately for each group. Second radioiodine uptake test was performed in patients who had uncertain TcTU (overlap with normal range). Results209 patients were included (54 euthyroid, 112 Graves’ disease, 29 toxic nodules and 17 subacute thyroiditis patients). Normal mean and range of TcTU were 1.5 +/- 1.1% and 0.17-4.8%, respectively. Mean TcTU was high in hyperthyroid patients and was extremely low in subacute thyroiditis patients, however, uncertain values was noted in about 30% of the patients. TcTU was uncertain in 39 hyperthyroid patients and in 10 subacute thyroiditis patients, while second radioiodine uptake was high in the former and extremely low in the latter.Test sensitivity was 68%, specificity was 100%, positive predictive value (PPV) was 100%, negative predictive value (NPV) was 52% and accuracy was 76%. ConclusionTcTU major disadvantage is the uncertainty seen in third of patients degrading test sensitivity and accuracy. We managed to overcome this uncertainty by adding second radioiodine thyroid uptake test. Accordingly, single visit TcTU was accurate and sufficient in about two thirds of patients while the remainder required second radioiodine uptake to reach accurate diagnosis.