The use of discriminatory values for thyroid uptake and free thyroxine index.

The distributions of 4 hour 132I neck uptake and 20 minute 99mTcO4 thyroid uptake in euthyroid patients were found to conform closely to a log normal distribution, from which a statistical normal range may be obtained. More accurate discriminatory values for determining thyroid status may be established by plotting intersecting distribution curves for hypo-, hyper- and euthyroid groups. Subdivision by age and by the presence or absence of a palpable thyroid reveals considerable variations from which a series of more accurate discriminatory values may be established for these subgroups. For Free Thyroxine Index (T4RT3 index) more accurate discriminatory values were also obtained by similar methods; while no significant variations related to age or palpable thyroid were observed, subdivision of the patients into two groups referred as suspected hypothyroidism and suspected hyperthyroidism yielded a further small improvement in accuracy.