Reference Percentiles and Changes over Time for Total Thyroxine in Preterm Infants: A Retrospective Cohort Study

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Claudia M Flores-Robles1, Ernesto Roldan-Valadez2,3, Nayeli Martínez-Cruz1

  • 1Department of Endocrinology, Instituto Nacional de Perinatología "Isidro Espinosa de los Reyes", Montes Urales 800, 11000 Mexico City, Mexico.

Diagnostics (Basel, Switzerland)
|July 17, 2020
PubMed

Insights

Preterm infants often have lower total thyroxine (tT4) levels, leading to false positives in congenital hypothyroidism screening. This study establishes tT4 reference ranges for Mexican preterm infants, suggesting lower screening cutoff values may be needed.

Area of Science:

  • Neonatal endocrinology
  • Public health screening programs

Background:

  • Hypothyroxinemia in preterm infants complicates congenital hypothyroidism screening.
  • Limited data exists on total thyroxine (tT4) reference ranges for preterm neonates.
  • Accurate screening requires population-specific reference values.

Purpose of the Study:

  • Establish reference percentiles for tT4 in dried blood spots of Mexican preterm infants.
  • Analyze tT4 concentration changes over time relative to gestational age.
  • Evaluate the impact of these findings on tT4-based newborn screening protocols.

Main Methods:

  • Retrospective cohort study including 1561 preterm infants.
  • Measurement of tT4 concentrations in dried blood spots.
  • Analysis of tT4 levels at different time points and gestational ages.

Main Results:

  • Established 10th percentile tT4 values for gestational ages 24-27, 28-30, 31-34, and 35-36 weeks.
  • Observed increasing tT4 concentrations in infants <30 weeks, stable levels in 31-34 weeks, and decreasing levels in 35-36 weeks.
  • tT4 levels changed significantly over the first few weeks of life and with corrected gestational age.

Conclusions:

  • Preterm infants exhibit distinct tT4 concentration patterns.
  • Current screening cutoff values for congenital hypothyroidism may need adjustment for preterm populations.
  • Lower tT4 cutoff values are suggested for preterm infants to reduce false positives.

Keywords:
central Hypothyroidismcongenital hypothyroidismdried blood spothypothyroxinemianewborn screeningpreterm infantsthyroxine

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