Incidence and clinical distribution of congenital hypothyroidism in Bolu Province, Türkiye: a four-year analysis of the National Newborn Screening Program

OBJECTIVE: We aimed to determine the incidence and etiological distribution of congenital hypothyroidism (CH) and evaluate the performance of newborn screening program in Bolu, a province in the Western Black Sea region of Türkiye. METHODS: Newborn screening data from 10,854 neonates born between March 2021 and March 2025 were analyzed. Capillary blood samples were collected on days 3-5 and analyzed. Infants with thyroid-stimulating hormone (TSH) levels >20 mIU/L initially or ≥5.5 mIU/L in both initial and repeat samples were recalled for venous confirmation. CH was diagnosed when free thyroxine was <0.7 ng/dL. RESULTS: Recall rate was 6.0%. Nineteen infants had CH (incidence, 1:571), including 13 (68.4%) with transient and 6 (31.6%) with permanent CH. All infants with initial TSH of 5.5-20 mIU/L had transient CH, while all permanent cases had initial TSH >20 mIU/L. A TSH threshold of ≥10 mIU/L reduced the recall rate to 1.1% but missed 5 transient CH cases (sensitivity, 73.7%). Threshold of ≥15 mIU/L reduced the recall rate to 0.3% but resulted in 10 missed transient cases (sensitivity, 47.3%). CONCLUSION: The incidence of CH and the recall rate in Bolu were higher than those reported in iodine-sufficient countries. Although the high recall rate may be partly attributable to the low TSH cutoff used in the screening program, relatively high proportion of transient CH warrants further investigation of regional iodine status. Increasing the TSH threshold may reduce the recall rate but may also decrease sensitivity and result in missed CH cases, particularly transient CH.