TSH Reference Ranges in Children by Age
The normal TSH reference range for children is approximately 0.6-4.5 μIU/mL for ages 3 years and older, though age-specific ranges are critical in early life when TSH values are physiologically higher, particularly in neonates and infants. 1
Age-Specific TSH Reference Ranges
Neonates and Infants (Day 14-30 of Life)
- TSH: 1.90-10.34 mIU/L (2.5th-97.5th percentile) 2
- This range is substantially higher than older children and adults, reflecting normal physiological variation in early life 2
- Values show wide spread immediately after birth, rapidly decreasing within the first 2 years of life 3
Early Childhood (Ages 2-7 Years)
- TSH: 0.10-5.9 μIU/mL (mean 2.2 μIU/mL) 4
- Reference range width becomes fairly stable after approximately age 4 years 3
- TSH upper reference limits are higher in early childhood and decrease toward adulthood 5
School Age and Adolescence (Ages 9-16 Years)
- TSH: 0.20-6.1 μIU/mL (mean 2.3 μIU/mL) 4
- Lower and upper limits steadily decline, essentially reaching or approximating healthy adult values by age 18 years 3
Practical Clinical Range (Ages 3+ Years)
- TSH: 0.6-4.5 μIU/mL is the commonly cited range for children aged 3 years and older 1
- In general practice, 0.45-4.5 μIU/mL is frequently used across different age groups, as differences are relatively small beyond early childhood 1
Critical Interpretation Guidelines
When to Treat Based on TSH Values
- TSH >10 μIU/mL: Treatment with levothyroxine is generally warranted regardless of symptoms 1
- TSH 4.5-10 μIU/mL: Management should consider symptoms, presence of thyroid antibodies (TPO-Ab), and other risk factors 1
- Mildly elevated TSH (10-20 mIU/L) in infants: Often normalizes on follow-up; consider monitoring first rather than immediate treatment 2
Essential Diagnostic Approach
- Always interpret TSH with free T4 levels to distinguish subclinical hypothyroidism (normal free T4) from overt hypothyroidism (low free T4) 1
- Repeat testing in 3-6 weeks is recommended before initiating therapy, as transient TSH elevations are common in children 1
- Test for thyroid peroxidase antibodies (TPO-Ab) if TSH is elevated, as positive antibodies indicate autoimmune etiology with higher risk of progression 1
Important Clinical Caveats
Factors Affecting TSH Interpretation
- TSH levels can be transiently affected by acute illness, certain medications, iodine exposure from CT contrast, and non-thyroidal illness 6, 7
- TSH secretion can vary by as much as 50% day-to-day, with up to 40% variation in serial measurements 6, 7
- Serial measurements are essential to establish true thyroid dysfunction 6, 7
Assay-Specific Variations
- Reference intervals vary significantly between different manufacturer assays and laboratory platforms 6, 7
- Each laboratory should ideally establish its own reference intervals using the specific immunoassay platform employed 6, 7
- Using adult TSH reference ranges in pediatric populations would result in overdiagnosis of hypothyroidism in children, particularly neonates and young children 6, 7
Special Populations
- Children with type 1 diabetes: Screen TSH soon after diagnosis, then every 1-2 years if thyroid antibodies are negative 8
- Children on growth hormone therapy for CKD: Monitor TSH and free T3 levels every 3-6 months 8
- Gender differences are minimal; boys' and girls' mean serum thyroid hormone values substantially overlap in all age groups 4