Assessment of thyroid function and autoantibody in type 2 diabetes mellitus

ABSTRACT

The associations between type 1 diabetes mellitus [DM] and autoimmune thyroid disease and other autoimmune diseases have long been recognized. However, these associations in type 2 DM are not certain. The study was performed to assess the thyroid function and autoimmune thyroiditis by detection of thyroglobulin antibodies [TG-ab] and thyroid peroxidase antibodies [TPO-ab] in type 2 diabetes mellitus. The study included 50 patients with type 2 diabetes over 10 years duration and 20 control subjects. The study was performed at Al-Azhar University Hospitals for control or management of diabetic complications. Patients with non-thyroidal illness or drug therapy, which known to affect thyroid functions were excluded from the study. The subjects of this study were submitted to the following complete history and clinical examination, BMI, blood sugar, lipid profile, thyroid function test [FT3, FT4, and TSH], HbAlc and thyroid autoantibodies [Tg-ab and TPO-ab]. Twenty-six patients out of 50 having abnormal levels of TSH, 6 of them below the normal reference range, while the other 18 patients with elevated TSH levels. Patients with elevated TSH had significantly lowered serum FT3, FT4 and elevated levels of TPO-ab, TG-ab, HbAlc, disease duration and BMI when compared to those with normal TSH [p<0.01, for all]. Patients with decreased levels of TSH had significantly elevated levels of FT3, FT4, HbAlc and BMI when compared to those with normal TSH [p<0.01], but no significant changes were found in serum levels of autoantibodies. Interestingly the incidence of abnormal thyroid function and elevated thyroid auto-antibodies were significantly higher in patients treated by insulin [70%] versus those treated by oral hypoglycemic drugs [30%], [p<0.01]. Twenty two patients out of 50 [44%] had elevated TPO-ab levels, 13 of them have TSH abnormality, 12 of these 13 patients have subclinical hypothyroidism and one has subclinical hyperthyroidism. 25 patients of 50 [50%], have increased level of TG-ab, 18 of them have abnormal TSH values, 16 out of these 18 have subclinical hypothyroidism and two patients have subclinical hyperthyroidism. Serum level of TSH only was significantly higher in females than males [p<0.05]. Serum levels of autoantibodies were correlated positively with serum levels of TSH, BMI, HbAlc, disease duration and insulin therapy and correlated negatively with FT3 and FT4. Type 2 diabetes may be associated with alteration in thyroid function especially subclinical hypothyroidism that is not fully explained by the mere presence of antithyroid antibodies