TSH Reference Ranges in Children by Age
TSH reference ranges in children are significantly higher than adults and vary substantially by age, with the highest values in neonates and infants, declining progressively through childhood to reach adult ranges by late adolescence. Using adult reference ranges (0.45-4.12 mIU/L) in pediatric populations leads to overdiagnosis of hypothyroidism, particularly in neonates and young children who have physiologically higher TSH values 1, 2.
Age-Specific TSH Reference Ranges
Neonates and Young Infants (Day 14-30 of Life)
- TSH: 1.90-10.34 mIU/L (2.5th-97.5th percentile) 3
- This range is notably higher than adult values and reflects the physiologic adjustment period after birth 3
- Infants with mildly elevated TSH (10-20 mIU/L) typically normalize on follow-up without treatment, suggesting initial monitoring rather than immediate intervention 3
Early Childhood (2-7 Years)
- TSH: 0.10-5.9 microU/ml (mean 2.2 microU/ml) 4
- TSH reference ranges show wide spread in the first 2 years of life, rapidly decreasing and stabilizing by approximately age 4 years 5
- Values remain fairly stable throughout this age range with minimal gender differences 4
School Age to Adolescence (9-16 Years)
- TSH: 0.20-6.1 microU/ml (mean 2.3 microU/ml) 4
- After age 4 years, the lower and upper limits of TSH steadily decline, essentially reaching or approximating healthy adult values by age 18 years 5
- Boys' and girls' mean serum thyroid hormone values substantially overlap in all age groups 4
Critical Clinical Considerations
Assay-Specific Variations
- Reference intervals vary significantly between different manufacturer assays and laboratory platforms 1, 2
- Each laboratory should establish its own reference intervals using the specific immunoassay platform employed, as demonstrated by variations across Roche, Abbott, Siemens, and Beckman Coulter platforms 6
- Direct comparison of values across laboratories is problematic due to these platform differences 7
Factors Affecting TSH Interpretation
- TSH levels can be transiently affected by acute illness, certain medications, iodine exposure from CT contrast, and non-thyroidal illness 1, 2
- 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 1, 2
- Serial measurements are essential to establish thyroid dysfunction rather than relying on a single value 1, 2
Common Pitfalls to Avoid
- Do not use adult reference ranges in children, as this results in significant overdiagnosis of hypothyroidism, particularly in younger age groups 1, 2
- Avoid testing thyroid function during acute metabolic stress (hyperglycemia, ketosis, weight loss) as results may be misleading due to euthyroid sick syndrome 7
- If initial tests are performed during metabolic instability, repeat after achieving metabolic stability 7
- Be aware that during very early life (especially newborns), values range widely, making interpretation particularly challenging 5
Monitoring Recommendations in Specific Populations
Children with Type 1 Diabetes
- Screen with TSH soon after diagnosis 8
- Recheck every 1-2 years if thyroid antibodies are negative 8
- Monitor more frequently if symptoms develop or thyroid antibodies are present 8
Children with Chronic Kidney Disease on Growth Hormone
- Monitor TSH and free T3 every 3-6 months, or more frequently for young patients and those with advanced CKD 8
- Measure thyroid hormone levels (TSH and free T3) before initiating GH therapy 8