The thyroid stimulating hormone (TSH) is produced and secreted by the pituitary gland and stimulates the thyroid to produce T3 and T4. When TSH is elevated, low thyroid function may be indicated. If TSH is low it is indicative of high thyroid function. A study found that TSH was suppressed in all subjects after food, so fasting may be suggested although it is not reqired by Quest. Free T4 and Free T4 values did not change significantly after eating.

The thyroid gland produces and secretes T4, otherwise known as thyroxine. Proteins bind to T4 and carry it throughout the bloodstream. Once in the tissues, T4 is released from the proteins and is now free to convert into the more active form called T3. For this reason, many doctors believe that measuring free T4 is a more sensitive test for thyroid hormone production.

This test measures Zinc levels in red blood cells (RBC). Red blood cell (RBC) analysis is an invaluable method for assessing insufficiency or excess of elements that have important functions within cells or on blood cell membranes. It may be more accurate than testing Zinc in blood serum.