These thyroid labs will give a complete picture of your thyroid. The last 2 tests are the least important, but I feel they are still very important. The only reason why I measure which ones are least important is because your ordering provider may not want to run them unless they see an anamoly within the first 4 tests.
TSH: Thyroid Stimulating Hormone. Produced by the pituitary gland. This is the most common test for thyroid, and usually the only one a provider may order. This is not a reliable test alone to determine thyroid function or whether or not the cells are using the thyroid that is being produced.
T4-FREE: This is they thyroid hormone that is produced in greater amounts by the thyroid gland in response to the TSH signal. This is sometimes referred to as the “storage” thyroid hormone in the body. It is not the form that the cells “actively use” for metabolism, sleep, menstrual regularity, and more.
T3-FREE: This hormone is produced in less significant amounts in the thyroid and is referred to as the “active” form. When T4 is produced, it is transferred to other tissues and converted into T3. Small amounts of T4 are also converted into “reverse T3”. Reverse T3 also can bind to thyroid receptor sites on the cell, acting as a buffer, to ensure that not “too much” T3 is attaching to receptor sites, thus marking “hyperthyroidism” – too much active thyroid.
TPO: Thyroid peroxidase antibodies. These are produced when a person’s immune system mistakenly targets components of the thyroid gland or thyroid proteins, leading to chronic inflammation of the thyroid (thyroiditis), tissue damage, and/or disruption of thyroid function. If thyroid antibodies are found in the blood, at ANY level, it is an indication of Hashimoto’s Thyroiditis – an autoimmune disorder.
T3-Uptake: Reflects available binding sites for T3 to attach and be utilized.
Reverse T3: Reverse T3 and T3 compete for receptor sites on cells. This is described as “antagonists” of each other. If your thyroid receptor sites have reverse T3 blocking them up, then T3 cannot bind to your cells. The T3 floats around in the blood, looking like you have normal levels, but since it’s not binding to the cells, it cannot perform its functions within the body.
Note: The creation of thyroid hormone is dependent upon the body’s reserves of iodine and healthy fats. The conversion of T4 to T3 involves the use of Selenium and Zinc by the body. Nutritionally, it is important to review the intake of foods and supplements that can aid this conversion. Sometimes one or many of these labs will appear within the normal range, but it is important to look at all of them together for a complete picture.