Evaluation of the adequacy of levothyroxine replacement therapy in patients with central hypothyroidism

As there are few data on the evaluation of the adequacy of levothyroxine (L -T-4) therapy in patients with central hypothyroidism (CH), a prospective s tudy was performed to assess the accuracy of various parameters in the foll ow-up of 37 CH patients. Total and free thyroid hormones, TSH, and a series of clinical and biochemical indexes of peripheral thyroid hormone action h ave been evaluated off and on L-T-4 therapy. Samples were taken before the daily administration of L-T-4. In all patients off therapy, clinical hypoth yroidism and low levels of free T-4 (FT4) were observed, whereas values of FT3, total T-4, and total T-3 were below the normal range in 73%, 57%, and 19% of cases, respectively. Most of the indexes of thyroid hormone action w ere significantly modified after L-T-4 withdrawal and exhibited significant correlation with free thyroid hormone levels. During L-T-4 replacement the rapy, 32 patients had circulating levels of FT4 and FT3 and indexes within the normal range with a mean L-T-4 daily dose of 1.5 +/- 0.3 mu g/kg BW. De spite normal serum FT4, 3 patients had borderline high values of FT3 and a clear elevation of serum-soluble interleukin-2 receptor concentrations, sug gesting overtreatment. Low or borderline low FT4/FT3 levels indicated under treatment in 2 patients. The clinical parameters lack the required specific ity for the diagnosis or follow-up of CH patients. The L-T-4 daily dose sho uld be established, taking into account the weight, the age, and the presen ce of other hormone deficiencies or pharmacological treatment of CH patient s. In conclusion, our results indicate that the diagnosis of CH is reached at best by measuring TSH and FT4 concentrations. In the evaluation of the adeq uacy of L-T-4 replacement therapy, both FT4 and FT3 serum levels together w ith some biochemical indexes of thyroid hormone action are all necessary to a more accurate disclosure of over- or undertreated patients.