Serum Thyrotropin is a Better Predictor of Future Thyroid Dysfunction Than Thyroid Autoantibody Status in Biochemically Euthyroid Patients with Diabetes: Implications for Screening

AIM: To ascertain the predictive values of thyroid autoantibodies and thyrotropin (TSH) levels for subsequent thyroid dysfunction in patients with diabetes. METHODS: Review of records of 467 patients who had attended diabetes clinics for a mean of 6.1 years. Baseline autoantibody and TSH results and thyroid status at annual review were determined. RESULTS: Thyroid disorders were known in 29 patients (6.2%), and newly identified in 32 (6.9%), at presentation. Of 406 patients with normal baseline thyroid status, 24 (5.9%) developed thyroid dysfunction during 6.1 years of mean follow-up. Higher baseline TSH concentration was associated with subsequent hypothyroidism; a threshold of 1.53 mU/L, approximately defining the top quartile, provided 75% sensitivity and specificity. Both TSH greater than 1.53 mU/L and positive autoantibody status predicted thyroid dysfunction, but only TSH was significant in multivariable analysis (odds ratio, 7.74, p < 0.001). No overt thyroid dysfunction developed in 293 patients with baseline TSH levels less than 1.53 mU/l. CONCLUSIONS: Baseline TSH level may be a better predictor of thyroid dysfunction than thyroid autoantibodies in people with diabetes. Patients with TSH levels below the top quartile have a risk of thyroid dysfunction similar to the general population. It may be appropriate to stop annual thyroid screening in this group, although confirmation is required.