Reference range of thyroid hormones in normal Indian school-age children

There is an ongoing debate on narrowing the TSH reference range in adults. In view of the scarce data on normal values of thyroid function tests in children from India, we planned to establish a reference range for thyroid hormones in school-age children.

All children (N = 9527; 6-19 years) from six schools representing various zones of Delhi were evaluated for clinical evidence of goitre, thyroid ultrasound, serum free T3 (FT3), free T4 (FT4) and TSH and anti-thyroid peroxidase (anti-TPO) antibodies. From this sample, a reference population (N = 5122) was obtained by excluding those with a personal or family history of thyroid disease, use of thyroid medications, goitre, hypoechogenicity/nodularity on ultrasound or serum anti-TPO antibodies.

Thyroid hormone (FT3, FT4 and TSH) reference ranges were established for each year of life for the total and reference populations.

In the reference population, mean serum FT3 was in the range 4.19-4.84 pm/l for boys and 4.03-4.47 pm/l for girls, mean serum FT4 14.69-17.36 pm/l for boys and 14.32-15.88 pm/l for girls, and mean serum TSH 2.57-3.6 mIU/l for boys and 1.83-3.58 mIU/l for girls. For TSH, the 97th percentile was in the range 6.01-8.4 mIU/l for boys and 5.28-8.04 mIU/l for girls, suggesting that at least in children there may not be a need to reduce the upper limit of normal for serum TSH.

This study provides mean reference intervals for FT3, FT4 and TSH for each year of life for both the sexes separately using strict exclusion criteria.