Objective: Down syndrome is the most common chromosomal anomaly. Thyroid dysfunction occurs frequently in individuals with Down syndrome. In this study, it was aimed to evaluate the thyroid function tests of patients diagnosed with Down syndrome, who presented to the pediatric endocrinology polyclinic of our hospital.

Material and Method: The data of a total of 79 patients with Down syndrome who presented to the pediatric endocrinology outpatient department between December 2018 and February 2020 were evaluated retrospectively. From the medical records of the patients, it was recorded whether the levels of thyroid stimulating hormone (TSH), free thyroxine (fT4), anti-thyroid peroxidase (anti-TPO), and anti-thyroglobulin (anti-Tg) were previously measured. Patients with normal levels of TSH and fT4 were defined as euthyroid; patients with high levels of TSH and low levels of fT4 were diagnosed with overt hypothyroidism, and patients with high levels of TSH and normal levels of fT4 were diagnosed with subclinical hypothyroidism. The diagnosis of Hashimoto’s thyroiditis (HT) was made by the presence of the positivity of thyroid autoantibodies (anti-TPO and/or anti-Tg).

Results: A total of 79 patients, 42 (53.2%) male and 37 (46.8%) female, were included in the study. The median age of the patients was 5.16 (1.58-9.41) years. Overt hypothyroidism was found in 16 (20.2%) of the 79 cases included in the study, subclinical hypothyroidism was found in 28 (35.5%) and euthyroidism was found in 35 (44.3%). The presence of anti-TPO and/or anti-Tg was checked in 52 of the 79 patients. Thyroid autoanti-bodies were positive in 9 (17.3%) of these patients.

Conclusion: Thyroid dysfunction, especially subclinical hypothyroidism, is common in children with Down syndrome. Therefore, it would be app-ropriate to perform thyroid function tests at regular intervals in these patients.