Labs‎ > ‎

*Thyroid Testing

A thyroid function test measures the amount of thyroid stimulating hormone (TSH) as well free T4 and free T3 in the blood serum. A thyroid antibody test may also be necessary.
There are three common causes of inadequate amounts of thyroid hormone for normal metabolism. The most well-known one is primary hypothyroidism, in which there is a raised TSH and a low T4 and low T3. This is due to failure of the thyroid gland itself, possibly due to thyroid autoantibody disease, possibly due to toxic stress or iodine deficiency.

Another common cause of low thyroid function occurs at the pituitary gland. In this situation there is inadequate thyroid stimulating hormone (TSH) produced from the pituitary, which shows as a low or normal TSH, low T4 and variable T3. This condition is common in patients with chronic fatigue syndrome, where there is a general suppression of the hypothalamic-pituitary-adrenal axis.

The third type of hypothyroid disorder is due to poor conversion of T4 to T3. This requires enzymes and co-factors, in particular selenium, zinc and iron. In this condition there are normal or possibly raised levels of TSH, normal levels of T4 but low levels of T3. This requires micronutrients and also T3 to correct.

For patients in whom thyroid problems are suspected a TSH, a Free T4 and a Free T3 is required in order to gain the full picture. For the first test, thyroid antibodies should be included to rule out autoimmune thyroid disease.