Thyroid stimulating hormone (TSH) is released from the pituitary gland and stimulates the thyroid gland to release thyroid hormones T3 and T4. Measuring levels of TSH is one way to assay the function of a child's thyroid gland. Typically, levels of TSH are quite high immediately after birth, and fall to adult levels by school age. TSH levels in school-age children normally ranges from 0.6 to 5.5 microunits per milliliter of blood.
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Thyroid stimulating hormone (TSH) is the major mechanism by which the pituitary gland communicates with the thyroid gland. When the pituitary measures a change in the amount of thyroid hormones T3 and T4 in the blood, it releases more or less TSH to correct the levels. In a child with abnormal thyroid hormone levels, the TSH test helps a physician determine whether the problem is in the thyroid or pituitary glands.
For full term newborns, the range of normal TSH levels is quite large. TSH can vary between 1.3 and 16 microunits per milliliter of blood. After about a month, this range narrows to 0.9 to 7.7 microunits per milliliter, and by school age it decreases to 0.6 to 5.5 microunits per milliliter. This gradual decrease in TSH levels is normal, though levels of free thyroid hormone (T4) in the blood will remain relatively stable over the same time period.
TSH level is only one test to assay thyroid function. It is often coupled with measurements of the thyroid hormones themselves, T3 and T4, or TSH releasing hormone (TRH). All these tests together can help a physician identify exactly where a problem occurs in a patient suffering from abnormal thyroid function tests. The methods for measurement of these different hormones are different however, and since TSH requires only a simple blood draw, it is often the first line lab test.
Abnormal levels of TSH coupled with symptoms of change in thyroid function can help identify any of multiple thyroid disorders. Higher than normal levels of TSH in a child can indicate congenital hyperthyroidism, thyroid hormone resistance or TSH-dependent hyperthyroidism. Lower than normal levels can occur in hypothyroidism, TSH deficiency or as a result of taking certain medications.
Though the normal range of TSH values is large, changes withing the normal range can indicate thyroid dysfunction as well. Also, high TSH levels with normal thyroid function may indicate risk of hypothyroidism in the future. Consulting with your physician about TSH levels in your child will help determine the best course of action for either monitoring or treating thyroid function.