Essential Blood Tests for Thyroid Function: Understanding Hypothyroidism, Hashimoto’s, and Hormone Levels (T3, T4)

Thyroid hormones effect almost every organ in the body. In the muscles they increase development of type 2 (aka fast-twitch) muscle fibres to help you make fast and powerful movements. At the heart they increase heart rate, contractility, and cardiac output. They stimulate the respiratory centres in the brain to increase oxygenation in the lungs. They effect your digestion, skin, hair and are involved in fertility and menstruation. Thyroid hormones also have a notable effect on the metabolism. They increase basal metabolic rate, stimulate metabolism of carbohydrates and stimulate the building of proteins. All of this to say, if something is off with your thyroid function you will feel it. It can manifest as a wide variety of symptoms ranging from fatigue to constipation to palpitations to difficulty conceiving. If you think you are experiencing any symptoms of thyroid dysfunction it is absolutely worth it to inquire about testing your thyroid through bloodwork.

Odds are, if you have inquired with your doctor about testing your thyroid function they will have run a TSH on your blood work. TSH is a great screening value, and is used to define clinical hypothyroidism and decide if a thyroid hormone prescription is required. TSH is reflective of your thyroid function but it doesn’t give us the entire story. When working with patients in which we suspect thyroid dysfunction may be involved we often run a thyroid panel. This is a series of blood tests that give us the full picture of how your thyroid is functioning or why it may not be functioning properly. Here are tests run on a thyroid panel and what each one tells us:

TSH

TSH is the thyroid panel’s claim to fame. This is often the first screening test run and it is used to determine a diagnosis of “hypothyroidism”. TSH is actually not a hormone produced by your thyroid. It is produced by your brain and released into the blood so it can communicate to your thyroid gland. TSH tells your thyroid gland to synthesize and release thyroid hormones, T3 & T4. TSH binding to the thyroid cell also promotes renewal, differentiation and maintenance of thyroid cells, essentially keeping your thyroid gland healthy and happy! The amount of TSH we release is controlled by our circulating levels of T3 & T4 and indirectly by the health of our thyroid gland. Our brains can sense the amount of T3 & T4 in our blood, if the thyroid gland is not releasing enough of these then the brain will release more TSH in response. This is our body’s way of telling the thyroid to wake up and start making us more hormones! If we have enough thyroid hormones in circulation then the brain will also sense that, and release less TSH.

Free T3 & Free T4

T3 and T4 are the hormones produced and released by our thyroid gland in response to TSH. These are the guys responsible for going into all the cells in our body and carrying out the thyroid’s function. All the cells in our bodies that can respond to these thyroid hormones have thyroid hormone receptors. These receptors have a much higher affinity for T3 than they do for T4. Therefore T4 is mostly inactive. Enzymes located in our livers, kidneys, muscles and thyroid glands convert T4 to T3 in order to activate it, then T3 can carry out it’s function. Thyroid hormones are then degraded by the liver and excreted in the bile.

Low T4 levels are a common lab finding in thyroid disease. By testing both T3 and T4 we can see if the low T4 is a result of low production or if there is a difficulty converting T3 to T4. This helps us identify which pathway needs more support.

Anti-thyroid peroxidase (TPO) and anti-thyroglobulin (Tg) antibody

The most common cause of hypothyroidism in iodine-sufficient populations is Hashimoto’s thyroiditis. It is caused by autoimmune mediated destruction of the thyroid gland. When an antibody binds to something it signals the immune system to attack and destroy the thing it has bound to. In a healthy state this pathway is used to identify and destroy bacteria and viruses that cause infections. In autoimmune diseases we produce antibodies that trigger our immune system to attack our own cells. In Hashimoto’s thyroiditis, antibodies are produced that trigger the immune system to attack thyroid peroxidase and thyroglobulin. These are proteins used by the thyroid gland to produce thyroid hormones (T3 & T4). When the immune system attacks these proteins it damages the thyroid cells and decreased the output of thryoid hormones. Positive anti-TPO and anti-Tg antibodies on bloodwork are correlated with the active Hashimoto’s disease. Eventually, if enough cells are damaged, the thyroid hormone production will be so low that we see a low T4 on bloodwork. The brain will sense this and try to correct it by producing more TSH, so we see a high TSH on bloodwork.

Having a deep understanding of your own bloodwork results is so important and empowering. With more knowledge you are able to take control of your health and make informed decisions about your treatment. This is why, as naturopathic doctors, we prioritize taking time to explain lab results to patients and explain how they align with changes in your symptoms.

If you have a history of thyroid dysfunction, a strong family history of a thyroid condition or if you are experiencing symptoms of hypothyroidism it may be indicated to run a thyroid panel. This is something your naturopathic doctor can run on your bloodwork for you. Getting the full picture can take the confusion out of thyroid assessment and help to determine the right treatment plan for you!

Author:
Dr. Carmen Aguayo, ND

References: 

PMID: 29083758

PMID: 29763182

DOI:10.13140/RG.2.2.26853.24808

Summary and call to action:
Understanding your thyroid blood test results is crucial for managing thyroid health. Learn how these levels impact your well-being and take control of your thyroid health today.

Read the full article to gain valuable insights and tips on interpreting your thyroid blood tests, and talk to a naturopathic doctor about personalized approaches to support your thyroid health!