Thyroid-Stimulating Hormone Reference Ranges for Preterm Infants

Abstract

BACKGROUND AND OBJECTIVES: Many newborn screening (NBS) programs now perform repeat or serial NBS to detect congenital hypothyroidism. There is wide variation in thyroid-stimulating hormone (TSH) cutoffs used by NBS programs. Data on TSH reference ranges in preterm infants at increasing postnatal age are limited. Our study objective was to determine TSH reference ranges for preterm infants born at <32 weeks’ gestation. METHODS: We analyzed serial TSH levels on NBS performed on infants born between 22 and 31 weeks’ gestation from 2012 to 2016 in Wisconsin. The study cohort was divided into 2 groups (22–27 and 28–31 weeks), and TSH percentiles were defined from birth to the term equivalent gestational age. RESULTS: The study cohort consisted of 1022 and 2115 infants born at 22 to 27 and 28 to 31 weeks’ gestation, respectively. The 95th percentile TSH level for the group born at 22 to 27 weeks’ gestation gradually decreased and reached a nadir at ∼10 to 11 weeks. In contrast, for the group born at 28 to 31 weeks’ gestation, the 95th percentile TSH level reached a nadir at ∼5 to 6 weeks. At 3 to 4 weeks after birth, the 95th percentile TSH level ranged from 11 to 11.8 μIU/mL for the group born at 22 to 27 weeks’ gestation and ranged from 8.2 to 9 μIU/mL for the group born at 28 to 31 weeks’ gestation. CONCLUSIONS: Using a statewide cohort of preterm infants, we constructed TSH reference charts from birth to the term equivalent gestation for preterm infants born at <32 weeks’ gestation. Use of a single cutoff for all preterm infants might lead to misdiagnosis. The differences in TSH levels according to gestational-age categories might explain the increased frequency in congenital hypothyroidism diagnoses among preterm infants. These data are useful for defining age-adjusted NBS TSH cutoffs for preterm infants.