Recombinant TSH testing predicts persistent thyroid tumour

A single test using recombinant human thyroid stimulating hormone (rhTSH) to provoke thyroglobulin secretion after apparently successful surgery is a valuable predictor of persistent thyroid cancer up to five years later, a recent study has concluded.American endocrinologists investigated 107 patients who had differentiated thyroid carcinoma treated by total or near-total thyroidectomy and then checked by administration of rhTSH. In follow-up evaluations one to five years after surgery, the presence of residual cancer was assessed by measuring thyroglobulin levels during thyroid hormone suppression, after rhTSH, and/or after thyroid hormone withdrawal. Patients were classified on the basis of the baseline rhTSH test as having thyroglobulin levels less than 0.5 ng/ml, 0.6-2.0 ng/ml, or exceeding 2.0 ng/ml. Persistent tumour was subsequently identified in 1.6% of the first group, 5.5% of the second, and 80% of the third."A single rhTSH-thyroglobulin of more than 2 ng/ml predicts persistent tumour, while no value entirely precludes future recurrence," the report concluded. "Repeated TSH-stimulated studies are appropriate for patients at risk of recurrence, especially those with an rhTSH-thyroglobulin greater than 1 ng/ml." However, in the patients with an rhTSH-stimulated thyroglobulin less than 0.5 ng/ml, 98% would be completely free of residual tumour. In this large group, aggressive TSH suppression, frequent imaging and TSH-stimulated thyroglobulin testing were unnecessary.It was important that tests for thyroid cancer had a high negative predictive value because it reassured both patients and doctors that the tumour had been successfully eradicated. This reduced the complexity and cost of follow-up, and allowed thyroid replacement therapy to be reduced to levels that avoided complications of subclinical thyrotoxicosis. Repeatedly withdrawing thyroxine to allow testing for residual thyroid function was poorly tolerated by many patients as they had to suffer hypothyroid symptoms during the process.Reference...