Control of Thyroid Dysfunction in Spanish Population Registered in the Primary Care Clinical Database: An Analysis of the Proportion of Patients with Thyrotropin Values Outside the Reference Range.

Inadequate control of thyroid dysfunction is common and has deleterious health consequences. Our objective was to determine the prevalence of TSH values outside the reference range, as an indicator of inadequate control of hypothyroidism and hyperthyroidism in patients undergoing treatment for thyroid dysfunction in Spain. An observational, retrospective, non-interventional study was conducted using the Primary Care Clinical Database (BDCAP). Patients treated with thyroid hormone for hypothyroidism and with antithyroid drugs for hyperthyroidism were identified. We assessed serum TSH concentration, considering values from 0.4 to 4.0 mU/l as the reference interval. We found 360 313 people with hypothyroidism on thyroid hormone replacement and 9239 with hyperthyroidism on antithyroid drugs therapy. TSH values outside the reference range in hypothyroid subject were detected in 126 866 (35.20%) people, of whom 107 205 (29.75%) had TSH>4.0 mU/l, suggesting inappropriately low doses of levothyroxine, and 19 661 (5.46%) had TSH<0.4 mU/l, suggesting inappropriate over replacement. In the hyperthyroid group, TSH values outside the reference range were observed in 4252 (46.02%) patients. There were 2833 (30.66%) patients with TSH<0.4 mU/l, suggesting undertreatment, and 1419 (15.36%) with TSH>4.0 mU/l, suggesting overtreatment with antithyroid medication. People over 65 years of age had a lower frequency of undertreatment of hypothyroidism and a lower frequency of overtreatment and undertreatment of hyperthyroidism. In conclusion, our results suggest that inadequate control of thyroid dysfunction, due to its high frequency and its consequences for health, is a public health problem that should be addressed by clinicians and health authorities.