THYREOTROPIN LEVELS IN DIABETIC PATIENTS ON METFORMIN TREATMENT

Objective: A retrospective study to evaluate the changes in TSH concentrations in diabetic patients treated or not treated with metformin and/or L-thyroxine (L-T4). Methods: Three hundred and ninety three euthyroid diabetic patients were divided into three groups on the basis of metformin and/or L-T4 treatment: Group (MK/LK), 119 subjects never treated with metformin and L-T4; Group (MC/LK), 203 subjects who started metformin treatment at recruitment; and Group (MC/LC), 71 patients on L-T4 who started metformin recruitment. Results: The effect of metformin on serum TSH concentrations was analyzed in relation to the basal value of TSH (below 2.5 mIU/l (Q1) or between 2.51 and 4.5 mIU/l (Q2)). In patients of group MC/LC, TSH significantly decreased independently from the basal level (Q1, from 1.45G0.53 to 1.01G1.12 mU/l (PZ0.037); Q2, from 3.60G0.53 to 1.91G0.89 mU/l (P!0.0001)). In MC/LK group, the decrease in TSH was significant only in those patients with a basal high-normal serum TSH (Q2: from 3.24G0.51 to 2.27G1.28 mU/l (PZ0.004)); in MK/LK patients, no significant changes in TSH levels were observed. In patients of group MC/LK showing high-normal basal TSH levels, a significant decrease in TSH was observed independently from the presence or absence of thyroid peroxidase antibodies (AbTPO; Q2 AbTPO C: from 3.38G0.48 to 1.87G1.08 mU/l (P!0.001); Q2 AbTPOK: from 3.21G 0.52 to 2.34G1.31 mU/l (P!0.001)). Conclusions: These data strengthen the known TSH-lowering effect of metformin in diabetic patients on L-T4 treatment and shows a significant reduction of TSH also in euthyroid patients with higher baseline TSH levels independently from the presence of AbTPO.