Thyroid Testing Reviewed

Worried there may be something wrong with your thyroid? You’ve have symptoms that might suggest it, like: fatigue, sensitivity to cold, constipation, weight gain, dry skin, sugar/carb cravings, muscle weakness or poor exercise performance and recovery, joint pain and stiffness, thinning hair, mild depression and increasing brain fog. However, you’ve been to your doctor, they ran a TSH and told you your thyroid function was fine. Sound familiar? It’s not (entirely) your doctor’s fault. You have to understand the model or the lens they’re looking through. They’re looking for disease, not necessarily dysfunction. Especially when talking about thyroid function, there’s a vast spectrum of dysfunction that can occur years before disease sets in. This post will discuss the various types of thyroid tests, what they mean and when to run them.


Thyroid Stimulating Hormone (TSH):
This hormone is released by the pituitary gland in your brain and triggers the production of an enzyme necessary to create thyroid hormones T3 and T4. This enzyme is called thyroid peroxidase (TPO) and it combines thyroglobulin, iodine and hydrogen peroxide. Your brain can sense when these hormone levels drop and it will increase the production of TSH, which will stimulate the thyroid to make more T4 and T3. This is why on labs, TSH usually has an inverse relationship with T4 and T3. When T4 and T3 levels are low, TSH should be elevated and vice versa. TSH testing is the most commonly utilized method for assessing thyroid function. Because elevated levels of TSH generally suggest that your thyroid is sluggish and not responding well, many physicians use TSH as the sole method of diagnosing thyroid conditions. Unfortunately, this isn’t a complete look at function and can lead to years of misdiagnosis or suboptimal function. In addition, the reference range by most labs is skewed. Most conventional endocrinology organizations now consider <2.5 to more normal.

Free T4 (Thyroxine):
Thyroxine, or T4, is the main hormone produced (about 93%) by the thyroid. However, it’s an inactive storage form of thyroid hormone, which means it does nothing for your metabolism. However, it is important as it indicates how much thyroid hormone is available to be converted into the active thyroid hormone, T3. Testing the amount of T4 in your blood is vital in determining if your thyroid gland is working correctly.

Free T3 (Triiodothyronine):
Perhaps the best marker of thyroid function is Free T3. Only about 3% is produced by the thyroid, so we depend on most of our T3 to be converted from T4. Without proper levels of T3, your metabolism will become slow resulting in reduced energy levels, mental sluggishness, and difficulty focusing. Alternatively, elevated T3 levels can result in an increased heart rate, erratic sweating, heart palpitations and jitteriness. Decreased T3 levels can be due to poor thyroid function (hypothyroidism), in which T4 levels will be low as well, or poor conversion of T4 to T3. This conversion occurs by an enzyme produced mostly in the liver (about 60% through the glucoronidation and sulfation pathways), gut (20%) and muscles. Therefore, if you have problems with any of these organ systems, your conversion may be affected. Th quickest way I’ve seen patients improve this conversion is through exercise. In addition, when the body is stressed (emotional, calorie restriction, too much exercise, etc.), it may convert more T4 to reverse T3, which is discussed next.

Reverse T3 (Reverse Triiodothyronine):
Reverse T3, much like T3, is converted from T4. However, reverse T3 functions as an “anti-thyroid” hormone. It sits on the T3 receptor on a cell and blocks T3 from being able to dock there. If T3 can’t dock onto that receptor, it can’t initiate metabolic changes inside the cell. This is an adaptive response that has helped humans in the past survive. Think about it. If you were living several hundred years ago and you had been wondering around searching for food but had not eaten anything in a week, this is a good thing. It would slow your metabolic rate down and allow you to conserve energy. Because it was crucial to our survival in the past, this trait has been passed down genetically from generation to generation. In first world societies today, food is abundant but so is stressed. We may not be going through famines anymore, but our bodies get placed under incredibles stresses nonetheless. When stressed, our bodies know what to do in order to survive…conserve energy.

Thyroid Antibodies:
If you’re a woman with symptoms of hypothyroidism but have normal TSH, free T4 and free T3 levels, consider getting antibodies tested. The most common cause of hypothyroidism in women is Hashimoto’s, an autoimmune condition. There are multiple antibodies that should be tested when analyzing your thyroid including anti-TPO (Thyroid Peroxidase Antibody), anti-TG (Thyroglobulin Antibody) and TSI (Thyroid-stimulating Immunoglobulins). Elevated levels in these may indicate an autoimmune disorder such as Hashimoto’s or Graves’ Disease that could otherwise go unnoticed.

25-OH Vitamin D3:
Low vitamin D3 is associated with thyroid disorders and should be addressed.  Vitamin D levels play a very important role in immune regulation, calming down autoimmunity and keeping inflammation levels under control.

CBC & Complete Metabolic Panel with iron and ferritin:
These tests will look in detail at red and white blood cell counts, iron stores and liver and kidney function. Both iron-deficient and B12 deficient anemia are common findings in thyroid disorders. Also, remember 60% of T4 to T3 conversion takes place in the liver so you want to check for adequate liver function.

Elevated homocysteine levels is an indicator of poor methylation function, which also complicates thyroid function.  Homocysteine is an inflammatory byproduct of the metabolism of methionine. Nutrients such as vitamin B2, B6, folate and B12, magnesium and zinc are key for optimal homocysteine levels and healthy thyroid function.

High Sensitivity CRP:
C-Reactive Protein (CRP) is a non-specific indicator of inflammation. Inflammation impedes the T4-T3 conversion.

This isn’t a complete list of tests, but it does assess for most issues that come about pertaining to thyroid dysfunction.