Interpretation: Normal Thyroid Function
These thyroid function tests are normal for a 5-year-old child and require no treatment or further investigation at this time. 1
Laboratory Values Assessment
The reported values fall within expected pediatric reference ranges:
- TSH 3.18 µIU/mL is well within the normal pediatric range of 0.45-4.5 mIU/L, and comfortably below the upper limit of 4.12 mIU/L established by NHANES III data 2
- Free T4 1.4 ng/dL is within normal limits 2
- Free T3 6.5 ng/dL appears elevated on initial review, but this requires verification against the specific laboratory's pediatric reference range for this age group 1
Critical caveat: Pediatric TSH reference ranges differ significantly from adult ranges, and using adult reference ranges in children leads to overdiagnosis of thyroid disorders 1. Each laboratory must establish age-specific reference intervals using their specific immunoassay platform 1.
Clinical Context Considerations
Before accepting these results as definitively normal, verify the following:
- Confirm the laboratory's age-specific reference ranges for all three values, as reference intervals vary significantly between manufacturer assays and laboratory platforms 1
- Assess for acute illness or recent iodine exposure (such as CT contrast), as TSH levels can be transiently affected and vary by up to 50% day-to-day 1
- Review for symptoms of thyroid dysfunction, though the normal TSH and T4 make clinically significant thyroid disease extremely unlikely 2
Differential Diagnosis Exclusions
The normal TSH with normal T4 effectively rules out:
- Primary hypothyroidism (would show elevated TSH with low T4) 2
- Primary hyperthyroidism (would show suppressed TSH with elevated T4) 2
- TSH-secreting pituitary adenoma (would show elevated T4 with unsuppressed or elevated TSH, plus clinical thyrotoxicosis) 2
- Thyroid hormone resistance (typically presents with markedly elevated T4 and T3 with non-suppressed TSH) 2
Management Recommendation
No intervention is required. 2
- Do not initiate thyroid hormone replacement as there is no evidence of hypothyroidism 2
- Do not pursue additional thyroid testing unless new symptoms develop 1
- Reassure the family that thyroid function is normal 1
When to Reconsider Testing
Repeat thyroid function testing would only be indicated if:
- New symptoms emerge suggestive of thyroid dysfunction (growth failure, weight changes, fatigue, temperature intolerance) 1
- The child develops type 1 diabetes, which would warrant TSH screening every 1-2 years 1
- The child requires growth hormone therapy, which necessitates baseline thyroid assessment 1
Important pitfall to avoid: Do not repeat testing simply because of minor TSH fluctuations within the normal range, as TSH naturally varies by up to 40% in serial measurements 1. The current TSH of 3.18 µIU/mL represents optimal thyroid function and does not warrant monitoring 2.