Normal TSH Reference Ranges in Children by Age Using ELFA Method
Critical Limitation
Specific reference ranges for TSH measured by ELFA (Enzyme-Linked Fluorescent Assay) method are not available in the provided evidence, and laboratories must establish their own age-specific reference intervals using the exact analyzer and reagent system employed in their facility. 1, 2
Key Principle for Pediatric TSH Interpretation
Using adult TSH reference ranges (0.45-4.12 mIU/L) in children will result in overdiagnosis of hypothyroidism, particularly in neonates and young children who have physiologically higher TSH values. 2, 3
Age-Specific TSH Reference Ranges from Available Immunoassay Methods
While ELFA-specific ranges are unavailable, the following age-stratified ranges from validated immunoassay platforms demonstrate the critical age-dependent variation:
Neonatal Period (First 2 Weeks)
Childhood and Adolescence
Immulite 2000 Platform (2.5th-97.5th percentiles): 5
- TSH values show wide spread immediately after birth, rapidly decreasing within first 2 years
- After age 4 years, ranges stabilize but steadily decline toward adult values by age 18 5
ADVIA Centaur Platform: 6
- Upper normal limit for TSH is approximately 1 mIU/L higher than previously published pediatric values 6
ECLusys Platform (μU/mL): 7
- 4-6 years: 0.62-4.90
- 7-8 years: 0.53-5.16
- 9-10 years: 0.67-4.52
- 11-12 years: 0.62-3.36
- 13-14 years: 0.54-2.78
- 15 years: 0.32-3.00
Critical Implementation Requirements
Laboratory-Specific Validation
Diagnostic laboratories processing pediatric samples must use age-, analyzer-, and reagent-appropriate reference ranges established with the identical system used in their laboratory. 1 Reference intervals vary significantly between different manufacturer assays and laboratory platforms. 2, 3
Age Group Standardization
Laboratories should standardize age groupings (neonates, 1 month-1 year, 1-5 years, 6-10 years, 11-16 years) which reflect statistically different TSH distributions. 1
Consequences of Inappropriate Reference Ranges
Using incorrect reference ranges leads to misdiagnosis with significant consequences: 1
- Unnecessary repeat testing and additional investigations
- Cancellation of surgeries
- Inappropriate labeling of children with thyroid disorders
- Direct and indirect healthcare costs
- Adverse psychological impact on families
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, with day-to-day variation of up to 50%. 2, 3 Serial measurements are essential to establish true thyroid dysfunction. 2, 3
Timing Considerations
Avoid testing thyroid function during acute metabolic stress, as results may be misleading due to euthyroid sick syndrome. 8 If initial tests are performed during metabolic instability, repeat after achieving stability. 8
Practical Recommendation
In the absence of ELFA-specific pediatric reference ranges, your laboratory must either: (1) establish its own age-specific ranges using the ELFA platform with healthy pediatric populations, or (2) refer pediatric samples to a reference laboratory that has validated age-appropriate ranges for their specific assay system. 1 Using published ranges from different platforms (Cobas, Immulite, ADVIA Centaur, ECLusys) for ELFA results is inappropriate and risks diagnostic errors. 1, 9