Free T4 is usually elevated in hyperthyroidism, and lowered in hypothyroidism. Free or unbound T4 levels correspond to the level of hormone available for uptake and use by cells. Bound levels represent a circulating hormone, all of which may not be readily available to the body, because it can be affected by certain medications, illness, and physical changes such as pregnancy. Because the free levels of T4 represent immediately available hormone, free T4 is thought to be a better indicator of thyroid hormone status than total T4. Many factors may disrupt the balance of thyroid hormone production, including medications, allergies (wheat & gluten), anemia, poor gastrointestinal function, insulin resistance, bone metabolism, hormone imbalances, nutrient deficiencies such as selenium, decreased levels of Vitamin A & D and metabolic disruptors such as PCBs to name a few.
Test Preparation For Optimal Results:
If possible, have the lab collected early in the morning or shortly after waking. For comparison purposes, have subsequent labs collected close to the same time.
Disclaimer: Your health care provider should evaluate a deviation from normal ranges.