Measurement of serum TSH and thyroid hormones in the management of treatment of thyroid carcinoma with radioiodine

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Abstract
1. Serum levels of TSH, thyroxine (T4) and triiodothyronine (T3) have been measured during treatment and follow-up of patients with thyroid carcinoma. 2. Serum TSH and thyroid hormone levels were initially normal. Three weeks after total thyroidectomy, TSH was elevated in about 50% of patients and after a subsequent therapy dose of 131I it exceeded 30 mU/l in 90% of patients. Occasionally, TSH did not rise until after the second dose of 131I. Low serum T4 and T3 concentrations were associated with the increase of TSH. 3. Withdrawal of 1-thyroxine replacement treatment in athyreotic patients for four weeks before test doses of 131I, led to falls of serum T4 and T3 concentration and a progressive rise of serum TSH after the first weeks but there was considerable variation in the final level reached. In the majority, values greater than 30 mU/l were attained despite some patients having received l-thyroxine for many years. A few patients on prolonged thyroxine maintenance had little or no increase i...