OR28-06 Thyroid Stimulating Hormone Reference Intervals For the First Year of Life

Abstract Disclosure: Z. Lu: None. N. Heather: None. E. Lim: None. A. McNeil: None. P. Coates: None. J. Smith: None. J. Hewitt: None. Hypothyroidism in infancy has potential for neurocognitive harm if untreated, is often asymptomatic, and can only be confirmed by biochemical testing. Dynamic physiological changes in thyroid function after birth necessitate the use of age-specific thyrotropin (TSH) reference intervals (TSHRI) to avoid delayed treatment and negative outcomes. Unfortunately, previously published TSHRI reference ranges for use in infants have been limited by study sample size and inappropriate age-partitioning, particularly in the first month of life. In the absence of international consensus on definitive age partitioned TSHRI for infants, we have recently conducted the largest methodical study of TSHRI to date, to define appropriate age partitioning reflecting the physiological changes in TSH in infancy. We aim to establish definitive TSHRI based on these age partitions for the major internationally utilised analytical assays: Beckman Dxl, Siemens, and Abbott Architect. TSH data from infants aged 0-1 year were extracted in a large multi-centre study. Results from 22,931 infants were included in the analysis after exclusion of TSH results from infants with more than one TSH measurement, TSH <0.01 or >50 mIL/L, known thyroid disease, severe illness, or premature birth. TSHRI were determined using the 2.5th and 97.5th percentiles of TSH values in each age partition. The TSHRI (n) for the age partitions of age 0-1 day, 2 days, 3 days, 4-13 days, 14-89 days, and 90-365 days were: 2.6-39.8 (122), 1.8-14.9 (172, 1.1-10.3 (242), 1.2-8.5 (2476), 1.1-7.8 (1398) and 0.6-5.7 (999) mIU/L respectively for the Beckman method; 1.5-38.9 (288), 1.1-15.3 (352), 1.0-13.1 (453), 0.9-8.5 (4638), 0.8-8.1 (3613) and 0.6-6.6 (3740) mIU/L respectively for the Siemens method; and 0.8-39.0 (102), 1.1-16.5 (142), 0.7-11.2 (195), 0.6-8.2 (1178), 0.9-7.0 (1146) and 0.6-4.6 (1675) mIU/L respectively for the Abbott method. No difference was observed between male and female infants. This is the first study to define TSHRI in infancy using a standardised approach and robust statistics across multiple major analytical methods. We define specific age partitions and their associated reference intervals for definitive international use within newborn screening programs and clinical diagnostics for testing of infant thyroid function. Presentation: Monday, July 14, 2025