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Reference ranges for newer thyroid function tests in premature infants
L M Adams1, J R Emery, S J Clark
1Department of Pediatrics, Loma Linda University School of Medicine, California.
Insights
This study establishes crucial thyroid function reference ranges for premature infants, using new assays for free thyroxine (T4) and thyrotropin. These findings provide essential data for monitoring thyroid health in preterm neonates.
Area of Science:
- Neonatal endocrinology
- Pediatric thyroid function testing
Background:
- Thyroid function assays have advanced, necessitating updated reference ranges for specific populations.
- Premature infants have unique physiological characteristics that influence thyroid hormone levels.
Purpose of the Study:
- To establish reference ranges for serum free thyroxine (T4) and thyrotropin in premature infants.
- To provide updated thyroid function data for neonates born between 25 and 36 weeks of gestational age.
Main Methods:
- Serum free T4 was measured using direct equilibrium dialysis.
- Serum thyrotropin was quantified via a sensitive immunometric method.
- 104 preterm infants (25-36 weeks gestational age) were studied within the first week of life.
Main Results:
- Free T4 levels positively correlated with gestational age (p < 0.0001).
- Two distinct reference ranges for free T4 were established: 6.4-42.5 pmol/L (31-36 weeks) and 16.7-60.5 pmol/L (25-30 weeks).
- A single reference range for thyrotropin (0.5-29 mU/L) was determined, also showing a positive correlation with gestational age (p < 0.001).
Conclusions:
- This study successfully established reference ranges for thyroid function tests in preterm infants.
- The findings extend current knowledge and provide vital clinical data for managing thyroid status in this vulnerable population.
Objective:
To establish reference ranges for recently developed assays of thyroid function in premature infants.
Methods:
We measured serum free thyroxine (T4) by direct equilibrium dialysis and serum thyrotropin by a sensitive immunometric method in 104 preterm infants (25 to 36 weeks of gestational age) during the first week of life.
Results:
The free T4 level correlated positively with gestational age (p < 0.0001; r2 = 0.09) and differed significantly between adjacent gestational age groups (p < 0.05). Free T4 concentrations (mean +/- SD) for the 25- to 27-, 28-to 30-, 31- to 33-, and 34- to 36-week groups were 18.0 +/- 5.2, 25.7 +/- 9.0, 30.9 +/- 9.0, 36.0 +/- 10.3 pmol/L (1.4 +/- 0.4, 2.0 +/- 0.7, 2.8 +/- 0.8 ng/dl), respectively. Two reference ranges for free T4 were determined, one for 25 to 30 weeks (6.4 to 42.5 pmol/L (0.5 to 3.3 ng/dl) and one for 31 to 36 weeks (16.7 to 60.5 pmol/L (1.3 to 4.7 ng/dl)). The logarithm of the value for thyrotropin correlated positively with gestational age (p < 0.001; r2 = 0.08); one reference range of 0.5 to 29 mU/L was determined for thyrotropin.
Conclusion:
This study extends information on thyroid function of preterm infants and establishes reference ranges for this population.