Serum concentration of free T3, free T4 and TSH in healthy children.

OBJECTIVE: It is rare that manufacturers report age-related FT3, FT4 and TSH normal ranges in healthy children. STUDY DESIGN: Using a solid phase time-resolved fluoroimmunometric method, we determined serum FT3, FT4 and TSH in 3,360 healthy children, age 2-16 years, that we grouped into two age ranges (2-7 yr and 9-16 yr). RESULTS: Boys' and girls' mean serum thyroid hormone values substantially overlap in all age groups. In the age range 2-7 yr, FT3, FT4 and TSH values were 0.10-0.67 ng/dl (mean 0.37 ng/dl), range 0.45-2.29 ng/dl (mean 1.18 ng/dl) and 0.10-5.9 microU/ml (mean 2.2 microU/ml), respectively. In the age range 9-16 yr, FT3, FT4 and TSH values were 0.11-0.53 ng/dl (mean 0.35 ng/dl), 0.69-1.69 ng/dl (mean 1.07 ng/dl) and 0.20-6.1 microU/ml (mean 2.3 pU/ml), respectively. CONCLUSION: Our results represent a useful set of reference values in children and can help physicians in the management of thyroid diseases.