Normal TSH Reference Ranges in Children by Age
TSH reference ranges in children vary significantly by age, with the highest values in neonates that progressively decline through childhood, reaching near-adult levels by adolescence.
Neonatal Period (Birth to 30 Days)
Days 3-7 of Life
The neonatal period shows the widest TSH ranges, with values rapidly declining after the initial postnatal surge 3. These early measurements are critical for congenital hypothyroidism screening, though interpretation can be challenging due to the physiological TSH elevation immediately after birth 3.
Days 13-15 of Life
- TSH: 1.4-8.6 mIU/L 1
By the second week of life, TSH values begin stabilizing but remain higher than older pediatric ranges 1.
Early Childhood (2-7 Years)
- TSH: 0.10-5.9 microU/ml (mean 2.2 microU/ml) 4
During early childhood, TSH reference ranges narrow considerably compared to the neonatal period, with the upper limit decreasing from approximately 10 mIU/L in neonates to around 6 mIU/L by age 2-7 years 4, 3.
School Age and Adolescence (9-16 Years)
- TSH: 0.20-6.1 microU/ml (mean 2.3 microU/ml) 4
By school age, TSH ranges become relatively stable and begin approximating adult values 4, 3. The lower limit remains consistent at approximately 0.2 mIU/L, while the upper limit continues a gradual decline toward adult ranges 3.
Key Clinical Considerations
Age-Dependent Changes
The most dramatic changes in TSH reference ranges occur during the first 2 years of life, with rapid narrowing of the reference interval 3. After age 4 years, the ranges stabilize considerably, though the upper and lower limits continue to decline gradually until reaching adult values by approximately age 18 3.
Comparison to Adult Ranges
The commonly cited adult TSH reference range of 0.45-4.12 mIU/L 5 or 0.4-4.5 mIU/L 5 is inappropriate for children, particularly neonates and young children who have physiologically higher TSH values 1, 3. Using adult reference ranges in pediatric populations would result in overdiagnosis of hypothyroidism 3.
Gender and Ethnicity
Boys' and girls' mean serum TSH values substantially overlap across all pediatric age groups, making gender-specific reference ranges unnecessary 4. While TSH reference ranges vary somewhat by ethnicity in adults, these differences are relatively small and not considered clinically significant enough to require ethnicity-adjusted ranges in routine practice 5.
Assay-Specific Variations
Critical pitfall: Reference intervals vary significantly between different manufacturer assays and laboratory platforms 6, 2. At TSH concentrations around 4.0 mIU/L, intermethod differences can be approximately 1 mIU/L, which may affect clinical decision-making 7. Each laboratory should establish its own reference intervals using the specific immunoassay platform employed 6.
Clinical Application
Age-specific reference ranges have minimal impact on diagnosis in older children and adolescents, with reclassification rates of only 0.1-1.9% when using age-adjusted versus fixed cutoffs 7. However, in neonates and very young children, age-appropriate ranges are essential for accurate diagnosis 1, 3.
Factors Affecting TSH Interpretation
TSH levels can be transiently affected by acute illness, certain medications (dopamine, glucocorticoids, dobutamine), iodine exposure from CT contrast, and non-thyroidal illness 6. TSH secretion can vary by as much as 50% on a day-to-day basis, with up to 40% variation in serial measurements performed at the same time of day 5. Never rely on a single TSH value to establish thyroid dysfunction—serial measurements are essential 5.