The hypothalamic-pituitary-thyroid axis in type 1 diabetes: influence of diabetic metabolic control.

The influence of diabetic metabolic control on indices of thyroid function was studied in 9 euthyroid, insulin-dependent (Type 1) diabetics. During chronic poor metabolic control (mean fasting blood glucose 13 mmol/l and HbA1 concentrations 14.7%) serum T3 concentrations were low (P less than 0.01) while serum T4 and basal TSH concentrations were normal. After 6-8 weeks of improved metabolic control, mean HbA1 concentrations had fallen to 10.7% (P less than 0.01) and serum T3 concentrations had increased into the normal range. Serum T4 and basal TSH concentrations were unchanged. The serum TSH response to iv TRH remained normal throughout the study. In Type 1 diabetics, with chronic poor metabolic control, the serum T4 concentration and the TSH response to TRH are therefore appropriate indicators of thyroid function.