Exploring reference ranges for thyroid-stimulating hormone in neonatal screening tests for preterm infants: a 5-year...

Currently, the same thyroid-stimulating hormone (TSH) cutoffs are used for term and preterm infants. Our objective was to determine TSH reference ranges and cut-off values for preterm infants born at different gestational ages (GA), birth weight (BW), and postnatal age (PNA).

A retrospective analysis was performed on preterm infants who received neonatal blood screening tests (NBST) between October 2017 and December 2022. Newborns were classified based on GA, BW, and small-for-gestational-age (SGA) status. For each category, the 2.5th, 5th, 50th, 95th, and 97.5th percentiles of TSH levels were determined. The 97.5th percentile was established as the cutoff value for TSH screening. TSH reference thresholds were then established for different PNA periods.

Infants were categorized based on GA, BW, and SGA status. Through this categorization, it was discovered that there were disparities in the cut-off values of TSH among different groups. In particular, during the first four weeks after birth in preterm infants, the 97.5th percentile TSH level (screening cutoff), one of the key indicators in NBST, shows a sequential trend of initial decline, subsequent rise, and final decrease, which peaked at 7.38 μIU/mL in the third postnatal week.

TSH levels in preterm infants are influenced by GA, BW, and PNA, with SGA infants showing significantly higher TSH levels (P < 0.05). Developing condition-specific TSH reference ranges is essential for improving congenital hypothyroidism (CH) diagnosis and management.