The variations in thyroid function tests compatible with clinical euthyroidism after medical and surgical treatment for Graves' disease.

Eight widely used tests of thyroid function (clinical and biochemical) were performed simultaneously on 46 thyrotoxicosis patients who were clinically well at a standardised interval after medical or surgical treatment. The aim was to establish the range of thyroid function compatible with clinical normality. While clinical scoring systems gave broadly similar results between surgically and medically-treated patients, thyroid biochemistry showed major differences. Thus while 87% of medically-treated and 74% of surgically-treated patients were classified clinically euthyroid by the clinical indices devised by Crooks and Billewicz, the TRH test was exaggerated in 77% of the latter group but in only 13% of the former. On the other hand, half of the 26% of surgical patients with a clinical index suggesting hyperthyroidism had normal thyroid hormone levels and exaggerated TRH tests. No patient was categorised as clinically hypothyroid despite basal TSH levels as high as 21 mU/L (N : less than 5 mU/L) and T4 levels as low as 42 nmol/L (N: 70.150 nmol/L). Substitution of FT4 index for total T4 did not significantly alter the classification or ranking of patients in either treatment group. The early (20-minute) 132I uptake was normal in all but one case. We conclude that abnormal laboratory tests of thyroid function are found frequently after treatment in thyrotoxicosis patients with few or no clinical features of thyroid disturbance.