What Is A Full Thyroid Test?

TSH (Thyroid-stimulation hormone)

The initial and most widely used test measures the level of TSH. Changes in your body’s TSH level can be seen as an “early warning system”as they may occur before the actual levels of thyroid hormones are seen too high or too low. TSH is mainly used to regulate the amount of thyroid hormones – T3 (triiodothyronine) and T4 (thyroxine) that is produced by the thyroid gland. 

A high level of TSH indicates that your thyroid gland is not producing enough thyroid hormones (hypothyroidism). A low level of TSH indicates that your thyroid gland is producing too much thyroid hormone and is classified as hyperthyroidism. 

While TSH is the standard test that more clinicians will provide, it only provides insight into one part of your thyroid function. Therefore, it is not considered a full thyroid test on its own.

Free T3 (triiodothyronine) Test

One of the hormones that the thyroid produces is called T3 (triiodothyronine). Most of the T3 in the body is bonded to protein, however, the T3 that is not bonded and circulates freely is called free T3. The Free T3 Test measures the amount of nonbonded T3 in the body.

T3 tests are most often used to diagnose hyperthyroidism or the severity of hyperthyroidism. Individuals with elevated T3 levels might indicate issues such as:

• Graves’ Disease
• Hyperthyroidism 
• Silent Thyroiditis
• Thyrotoxic Periodic Paralysis
• Toxic Nodular Goiter

High levels of T3 might also indicate high levels of protein in the blood. A Free T3 test is crucial to measure the amount of free T3 in the body; however, it does not provide information by itself and is only considered a part of a full thyroid test.  

Free T4 (thyroxine) Test

T4 (thyroxine) is the inactive version of T3. The primary duty of T4 is to transport T3 to the proper organs throughout the body. T4 must be converted to T3 before it can be used. A Free T4 Test measures the amount of unbonded T4 available in the body. 

Elevated levels of T4 may indicate: 

• Thyroiditis 
• Toxic Multinodular Goiter 
• Too much iodine
• Too much thyroid replacement medication

Low levels of T4 may indicate:

• Hypothyroidism
• Dietary issues (iodine deficiency, fasting, malnutrition)
• Medications that affect protein levels

TPO Antibodies 

A TPO Antibodies Test measures the amount of Thyroid Peroxidase in the body. TPO (Thyroid Peoxidase) is an enzyme found in the thyroid gland that plays an important role in the production of thyroid hormones.

TPO essentially converts the iodine absorbed from our food to an active form of iodine that our body can use. Iodine is vital for the production of both T3 and T4. Elevated levels of TPO may indicate Hashimoto’s Thyroiditis. Hashimoto’s is an autoimmune disease where your immune system attacks your body’s healthy thyroid cells.  

It is vital to include TPO Antibodies in a full thyroid test as you could have high levels of TPO but still show normal TSH levels. Hashimoto’s Thyroiditis is the most common cause of hypothyroidism in the United States. With early detection, patients are more likely to be able to slow down the progression and better manage it. 

Reverse T3

Reverse T3 (rT3) is an inactive form of T3 and is the byproduct of T4. Though the importance of rT3 is widely debated, it can be an important marker in situations for patients that have undergone extreme trauma, stress, and/or surgery. Therefore, it is recommended as part of a full thyroid test. 

Tg (Thyroglobulin)

This test measures the level of thyroglobulin in your blood. Thyroglobulin is a protein that can be made by both normal and cancerous thyroid cells. Tg tests are most commonly used for cancer treatments to

• See if the cancer treatment was successful 
• See if cancer has returned after treatment 

If thyroglobulin levels stay the same or increase after treatment, it may mean there are still thyroid cancer cells in the body. If thyroglobulin levels decrease or disappear after treatment, it may mean there are no normal or cancerous thyroid cells left in the body.

Tg Antibody (TgAB)

This test measures the level of thyroid antibodies in the blood. This test is used to diagnose autoimmune disorders with the thyroid. 

Antibodies are proteins in the immune system that are meant to fight off foreign substances like viruses and bacteria. Sometimes antibodies will attack the body’s own healthy cells which can lead to an autoimmune disorder.