Age-specific thyroid hormone and thyrotropin reference intervals for a pediatric and adolescent population

Area of Science:

• Clinical Biochemistry
• Pediatric Endocrinology
• Laboratory Medicine

Background:

• Reliable reference intervals are essential for standardizing laboratory methods and ensuring accurate clinical interpretation.
• Measurement uncertainty (U) and reference change value (RCV) are critical for assessing the reliability and clinical significance of laboratory results.

Purpose of the Study:

• To establish reference intervals for serum thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4), and free T4 (fT4) in a pediatric population.
• To determine the measurement uncertainty (U) and reference change value (RCV) for these thyroid assays.

Main Methods:

• Analysis of laboratory data from 7581 children and adolescents (0-20 years).
• Subjects were categorized into nine age groups to define reference distribution percentiles (2.5th, 50th, 97.5th).
• Calculation of measurement uncertainty and reference change values for TSH, T3, T4, and fT4 assays.

Main Results:

• Thyroxine and free T4 levels were higher in early infancy compared to older age groups.
• Established 95th percentile reference values for T4 and T3, and 2.5th percentile for fT4, aiding in hyperthyroidism and hypothyroidism diagnosis.
• Serum TSH showed minimal age-related variation (97.5th percentile: 4.38-4.88 mIU/L).
• Assays exhibited approximately 20% measurement uncertainty.
• Serum TSH had a larger RCV (58.6%) compared to thyroid hormones (28.3%-34.7%) due to biological variation.

Conclusions:

• Established comprehensive reference intervals for TSH and thyroid hormones in pediatric populations.
• Provided measurement uncertainty values to ensure assay reliability.
• Determined reference change values to alert clinicians to significant clinical changes in thyroid hormone levels.