Reference ranges for analytes of thyroid function in children

Area of Science:

• Pediatric Endocrinology
• Clinical Chemistry
• Laboratory Medicine

Background:

• Accurate diagnosis of pediatric thyroid dysfunction relies on age-specific reference ranges for key thyroid hormones.
• Existing ranges may not adequately reflect physiological changes throughout childhood and adolescence.
• The Immulite® 2000 assay is widely used, necessitating validated reference values for its application.

Purpose of the Study:

• To establish age-specific reference ranges for serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) in a pediatric population.
• To characterize the age-related changes in these hormone reference ranges from birth through adolescence.
• To provide data supporting the use of tailored reference intervals for improved clinical interpretation in children.

Main Methods:

• Serum samples from 656 healthy children (newborn to 18 years) were analyzed using Immulite® 2000 assays for TSH, FT4, and FT3.
• Non-normally distributed data required using the 2.5th and 97.5th percentiles to define reference ranges.
• Age-related reference range curves were calculated using the linearity, median, and skewness method.

Main Results:

• Thyroid hormone reference ranges exhibited wide variation at birth, decreasing significantly within the first two years of life.
• Reference range width stabilized around age 4, with lower and upper limits progressively declining towards adult values by age 18.
• Significant age-dependent shifts were observed for TSH, FT4, and FT3, particularly in early childhood.

Conclusions:

• Age-specific reference ranges are essential for accurate interpretation of TSH, FT4, and FT3 levels in children.
• The wide variability in early life necessitates careful consideration when assessing thyroid function in infants and newborns.
• These established ranges facilitate prompt and reliable detection of pediatric thyroid dysfunction.