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Age-related changes in serum free thyroxine during childhood and adolescence
J C Nelson1, S J Clark, D L Borut
1Loma Linda University School of Medicine, California.
Insights
Serum free thyroxine (T4) levels change with age from infancy to adulthood. These age-related changes in free T4 and its relationship with thyrotropin indicate developmental shifts in thyroid regulation.
Area of Science:
- Endocrinology
- Pediatric Endocrinology
- Thyroid Research
Background:
- Thyroid hormones are crucial for growth and development.
- Age-related changes in thyroid hormone concentrations are not fully understood.
- Previous studies have not comprehensively evaluated serum free thyroxine (T4) across all pediatric age groups.
Purpose of the Study:
- To reevaluate age-related changes in serum free thyroxine (T4) from infancy to adulthood.
- To investigate the relationship between serum thyrotropin and free T4 concentrations across different age groups.
- To establish age-specific reference ranges for serum free T4.
Main Methods:
- Studied 536 healthy individuals aged 1 day to 45 years.
- Measured serum free T4 using direct equilibrium dialysis.
- Assessed serum thyrotropin via sensitive immunoassay and total T4 by radioimmunoassay.
Main Results:
- Serum free T4 concentrations showed significant age-dependent variations (p < 0.001) across distinct age intervals.
- Age-related reference ranges for free T4 were established.
- The relationship between thyrotropin and free T4 was complex, suggesting age-specific pituitary-thyroid regulation.
- No correlation between free T4 and total T4 was observed after 13 days of life.
Conclusions:
- Pediatric free T4 concentrations and their relationship with thyrotropin differ from adult patterns.
- Age-related changes in total T4 do not accurately reflect free T4 levels or thyroid function beyond the neonatal period.
Abstract:
The purposes of this study were to reevaluate age-related changes in the concentration of serum free thyroxine (T4) between early infancy and adulthood, and to study the relationship of serum thyrotropin to these changes in free T4. Five hundred thirty-six healthy infants, children, adolescents, and adults between 1 day and 45 years of age were studied. Serum free T4 was determined by direct equilibrium dialysis, thyrotropin by a sensitive immunoassay, and total T4 by radioimmunoassay. Free T4 concentrations were age dependent and differed significantly (p < 0.001) at 1 to 4 days, 2 to 20 weeks, 5 to 24 months, 2 to 7 years, 8 to 20 years, and 21 to 45 years of age. Corresponding free T4 concentrations (mean +/- SEM) were 48.1 +/- 1.5, 20.3 +/- 0.6, 17.0 +/- 0.4, 19.9 +/- 0.4, and 21.2 +/- 0.4 pmol/L (3.74 +/- 0.12, 1.58 +/- 0.05, 1.32 +/- 0.03, 1.55 +/- 0.03, 1.32 +/- 0.03, and 1.65 +/- 0.03 ng/dl), respectively. Age-related reference ranges were determined. Changes in the relationship between serum thyrotropin and free T4 were complex, indicating age-related changes in pituitary thyroid regulation. No correlation existed between concentrations of free T4 and total T4 after the first 13 days of life (r2 < 0.01). We conclude that (1) pediatric free T4 concentrations and free T4-thyrotropin relationships differ from those in adults and (2) age-related changes in total T4 do not indicate age-related changes in either free T4 or thyroid function, after 13 days of age.