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Updated: Oct 2, 2026
Biochemical Measurement of Neonatal Hypoxia
Published on: August 24, 2011
Serum free thyroxine concentration is not reduced in premature infants with respiratory distress syndrome
1Department of Pediatrics, Loma Linda University School of Medicine, CA 92350, USA.
Insights
Pituitary-thyroid function remains normal in premature infants with respiratory distress syndrome (RDS). Low total thyroxine (TT4) levels in these infants are due to reduced thyroxine (T4) binding, not altered thyroid function.
Area of Science:
- Neonatalogy
- Endocrinology
- Pediatric Respiratory Medicine
Background:
- Premature infants with respiratory distress syndrome (RDS) may exhibit altered thyroid hormone levels.
- Understanding pituitary-thyroid axis function is crucial for managing these vulnerable infants.
Purpose of the Study:
- To investigate pituitary-thyroid function in premature infants with RDS during the first postnatal week.
- To differentiate between true thyroid dysfunction and altered binding protein effects.
Main Methods:
- Serum free thyroxine (T4), total thyroxine (TT4), and thyrotropin were measured using advanced assays.
- 90 premature infants (45 with RDS, 45 controls) were studied within the first week of life.
- Infants with RDS received exogenous surfactant therapy.
Main Results:
- No significant differences in free T4 or thyrotropin levels were observed between RDS and control groups.
- Infants with RDS showed significantly lower total T4 concentrations (p < 0.001).
- Lower TT4 was attributed to reduced T4 binding to serum proteins, particularly in earlier gestations (p = 0.0075).
Conclusions:
- Pituitary-thyroid function is not altered in premature infants with RDS.
- The observed low total T4 state is solely due to reduced serum T4 binding, similar to acute nonthyroidal illnesses.
Objective:
We used improved methods of assay to determine whether pituitary-thyroid function is altered in premature infants with respiratory distress syndrome (RDS) during the first week of postnatal life.
Methods:
Serum free thyroxine (T4) was measured by direct equilibrium dialysis, total thyroxine (TT4) by radioimmunoassay, and thyrotropin by a sensitive immunometric assay in 90 premature infants (45 healthy control subjects and 45 with RDS) during their first week of life after 25 to 30 weeks of gestation. Infants in the RDS group received exogenous surfactant therapy.
Results:
Free T4 and thyrotropin concentrations of infants were not significantly different between RDS and control groups. As expected, infants with RDS had significantly lower serum total T4 concentrations compared with control infants (p < 0.001). This difference was present even after stratification for gestational age (25- to 27-week group, p = 0.012; 28- to 30-week group, p = 0.002). Lower total T4 concentrations were attributable to lower T4 binding to serum proteins among infants with RDS compared with control subjects, especially in the 25- to 27-week gestation group (p = 0.0075).
Conclusion:
These data indicate that pituitary-thyroid function is not altered in premature infants with RDS. The low total T4 state in these premature infants is attributable solely to reduced serum T4 binding, as is often seen in acute nonthyroidal illnesses.
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