Using a computerized method to measure 99mTc pertechnetate uptake for the assessment of thyroid function

This retrospective study evaluated thyroid function by the 99mTc pertechnetate uptake ratio, using computer software designed in our laboratory. We expected that this measurement could be a precise and accurate index. The following studies were performed on 187 patients: (1) 24-hour radioimmunoassay of serum thyroid hormones, including serum thyroxine, free T4, triiodothyronine, thyrotropin concentrations, and T3 resin uptake; (2) 99mTc pertechnetate thyroid imaging and uptake measurement; and (3) 24-hour 131I thyroid uptake. Based on the clinical findings and the results from the predescribed laboratory tests, we found that: (1) the mean value of the 99mTc pertechnetate thyroid uptake ratio in the euthyroid groups was 2.77 +/- 1.77% (mean +/- SD); (2) the correlation coefficient between the 99mTc pertechnetate thyroid uptakes and the 24-hour 131I uptakes of the euthyroid patients was 0.71; and (3) hyperthyroidism could be distinguished from euthyroid condition easily. By setting the upper limit of euthyroid 99mTc pertechnetate thyroid uptake at 6.31%, the diagnostic sensitivity was 92.9%, specificity 96.1%, and accuracy 95.6% in separating hyperthyroid from euthyroid patients. These values were similar to those determined by the 24-hour 131I uptake measurements. Thus, thyroid function can be evaluated simultaneously with a routine 99mTc pertechnetate thyroid scan. Both the patient time and cost can be saved with this method, since the measurement takes only 25 minutes. Decreased radiation exposure is another advantage of this method over the traditional 131I uptake measurement.