Background: National and international guidelines recommend thyrotropin (TSH) determination as the most sensitive test for detecting primary congenital hypothyroidism (CH) in newborn screening programs. A strategy of a second screening at 2 weeks of age, or 2 weeks after the first screening was carried out, is also recommended in preterm, LBW and VLBW neonates, twins, neonates admitted in NICU, and babies with specimen collection within the first 24 hours of life . However specific recommendations on the TSH cut off at 2 weeks of age are lacking, as well as specific reference intervals for TSH at this age. The aim of this study was to determine TSH reference intervals at 2-4 and 14-16 days of age in healthy term newborns.
Methods: Dried blood spot (DBS) samples were obtained from 70,962 healthy term newborns (>37 week Gestational Age) residing in Lombardia region and screened in 2015 at the Lombardia region Reference Laboratory for Neonatal Screening. A time resolved-fluoroimmunoassay (TR-FIA) method was used to detect TSH on DBS at the first (24 days) and second screening (1416 days). STATA 11.0 was used to analyze 2.5th, 50.0th, 97.5th, 99.0th, 99.5th percentiles for DBS-TSH.
Results: No significant difference was found between the 2.5th percentile of DBS-TSH at 24 days (0.59 mU/L; 95% CI: 0.590.60) and the same percentile at 1416 days (0.58 mU/L; 95% CI: 0.560.59); whereas the 50.0th percentile was significantly higher at 24 days (2.06 mU/L; 95% CI: 2.052.07) than at 1416 days of life (1.52 mU/L; 95% CI: 1.511.54), as well as the 97.5th percentile (6.24 mU/L; 95% CI: 6.196.29 vs 4.04 mU/L; 95% CI: 3.914.21), the 99.0th percentile (7.60 mU/L; 95% CI:7.497.73 vs 5.10 mU/L; 95% CI: 4.805.64), and the 99.5th percentile (8.80 mU/L; 95% CI: 8.659.00 vs 6.64 mU/L; 95% CI: 6.117.55).
Conclusions: Our data showed that marked changes occur in concentrations of TSH during the first 2 weeks of life with DBS-TSH concentrations significantly higher at 24 days than at 1416 days of life. These results have implications for selection of age-related cut off values of DBS-TSH at screening (24 days) and re-screening (1416 days) to correctly identify newborns at risk for CH.
References: 1. Leger J et al. J Clin Endocrinol Metab 2014, 99:363-384. 2. Cassio A et al. J Endocrinol Invest 2013, 36: 195-203. 3. CLSI document I/LA31-A, Clinical and Laboratory Standards Institute; 2009.
27 - 29 Sep 2018
European Society for Paediatric Endocrinology