Serum thyrotrophin concentration: an unreliable test for detection of early hypothyroidism after thyroidectomy.

Three groups of patients who had undergone subtotal thyroidectomy for Graves's disease, toxic multinodular goitre, or euthyroid multinodular goitre 12 to 15 years before and in whom a normal serum thyroxine (T-4) level was found were each divided into two subgroups on the basis of a normal or a raised serum thyrotrophin concentration. There was no difference in mean serum T-4 concentration between patients with normal and those with raised serum thyrotrophin concentrations, and the values were similar to the mean T-4 values of the normal population. The mean serum triiodothyronine values of all groups were higher than normal, but the mean values of the groups with a normal and a raised serum thyrotrophin were similar. After thyroidectomy a mildly raised serum thyrotrophin does not in itself indicate the presence of hypothyroidism.