Pediatric reference intervals for thyroid hormone levels from birth to adulthood: a retrospective study

Area of Science:

• Endocrinology
• Pediatric Endocrinology
• Clinical Chemistry

Background:

• Accurate interpretation of pediatric thyroid hormone measurements requires age- and sex-specific reference intervals.
• Limited data exists for pediatric reference values of TSH, fT3, and fT4.
• Reference intervals are known to be method- and population-dependent.

Purpose of the Study:

• To establish reference intervals for serum TSH, fT3, and fT4 in children from birth to 18 years.
• To assess potential sex differences in these thyroid hormone levels.
• To provide updated reference data considering analytical methods and population variations.

Main Methods:

• Retrospective analysis of 2,194 thyroid hormone tests from a pediatric population.
• Exclusion of individuals with conditions or medications affecting thyroid function.
• Measurement of fT3, fT4, and TSH using the Advia(R) Centaur automated immunoassay system.

Main Results:

• Final sample sizes: 1,209 for TSH, 1,395 for fT3, and 1,229 for fT4.
• Median concentrations of fT3, fT4, and TSH were highest in the first month of life, declining with age.
• Males exhibited significantly greater mean fT3 concentrations than females (p < 0.001), with no sex differences found for TSH and fT4.

Conclusions:

• Thyroid hormone levels change significantly during childhood, rendering adult reference intervals inapplicable.
• Established reference intervals differ from previous studies, potentially due to analytical methods, population characteristics, or geographic factors.
• These findings underscore the importance of age- and sex-specific reference intervals for pediatric thyroid hormone assessment.