Assessment of the combined usefulness in thyroid function testing of the triiodothyronine resin-sponge and 24-hour iodine uptakes.

Iodine and resin sponge uptake tests have been performed upon 124 consecutive patients referred for thyroid studies. Neither test alone could correctly identify all cases of thyrotoxicosis or myxoedema, but when considered in combination diagnostic efficiency was much improved. This combination of tests is shown to be especially useful in the investigation of patients with changes in body iodine pools or thyroxine-binding globulin levels. Reasons are given for regarding this pair of tests as being more generally useful than any of the other possible combinations at present available. The resin sponge test kit was found to be satisfactory both technically and in respect of cost.