It is likely that you received Hashimoto’s diagnosis based on your values of TSH and free thyroxine, otherwise known as fT4. These are the most common labs ordered to evaluate thyroid function, and we will speak briefly about them. While these tests are quite reliable, there are a few more that can be looked at, even before diagnosis that can give us signs that Hashimoto’ may be imminent. We need to take all of these tests into account to give a holistic perspective on the thyroid. 

TSH and fT4

These are the main players in diagnosing an underactive thyroid. TSH is an average of how well your thyroid has been working over the past month, from the perspective of the pituitary gland, which oversees thyroid function. T4 or thyroxine is the body’s main reserve of thyroid hormone, and this can be in the form of free form, meaning unbound and free in the bloodstream, or bound to proteins which prevent T4 from being active in the tissues. The level of free T4 in the blood is quite tightly regulated, should remain stable over time, and therefore is a consistent marker for the health of the thyroid. In Hashimoto’s disease, there will often be fluctuations in free T4 prior to there being changes in TSH. 

T3 and Free T3

While our reserve of thyroid hormone is stored in T4, it needs to be converted to T3 to be metabolically active in the body. While T4 remains relatively stable, T3 often fluctuates based on the body’s metabolic needs. The active part of T3 that binds to thyroid receptors in the body is called free T3. There are many cofactors necessary for the conversion of T4 to T3, and if these are lacking, then patients may have a normal fT4 and TSH, but a low fT3, which can manifest with all the symptoms of an underactive thyroid. For a complete panel, it is best to check total T4 and T3, as well as fT4 and fT3. 

Reverse T3

When we have our total supply of T4, and it is not efficiently converted to T3, then there is also another reaction that can happen: the conversion of T4 to reverse T3. Reverse T3 is the metabolically INACTIVE form of T3, and it blocks the action of T3 by binding to the same thyroid receptors as T3. Many lifestyle factors, such as gut issues, high cortisol levels, lack of sleep, and stress, can lead to increased reverse T3 levels. Therefore, for a holistic approach to thyroid disorders, this is a very important blood test to have. 

Thyroid Antibodies

One of the main differences between Hashimoto’s disease and an underactive thyroid is that there is a significant autoimmune component in Hashimoto’s disease, where our own immune cells attack the thyroid. The way we measure the degree of attack is thru the number of different antibodies produced. Once antibodies are produced, this gives a signal to specific immune cells to attack the thyroid. 

The most common antibody produced is called thyroid peroxidase antibody, or TPO antibody. It prevents the uptake of iodine, which is managed by the thyroid peroxidase enzyme and is the first step in producing thyroid hormone. The second most common antibody is the thyroglobulin antibody, which is produced against thyroglobulin, a protein that makes up about half of the thyroid gland. Slightly less common in Hashimoto’s and more common in autoimmune hyperthyroidism, are TSH receptor antibodies. These antibodies tend to hijack the directions that the thyroid gets from the pituitary gland, causing inappropriately more thyroid hormone to be produced. Whilst this is more often associated with Grave’s disease, it can also be presented in the first stages of Hashimoto’s, where there is a hyperthyroid state that then is followed by the destruction of thyroid cells. Ideally, we would like to have all antibodies tested on a blood test, both for diagnosis and for monitoring the degree of autoimmunity in thyroid disease. 

Related Blood Tests

While we focus on the thyroid, it is also important to remember that the thyroid being sick is a manifestation of overall health in the body. Therefore, it is worth getting a more holistic and wide view of the body from laboratory tests. Therefore, we recommend that basic blood panels, such as full blood count, ferritin, renal and liver function, and CRP are also tested as part of a routine thyroid assessment. Moreover, high cholesterol and insulin resistance are more prevalent in Hashimoto’s patients, so a lipid panel, HbA1C and fasting glucose and insulin are also important markers to monitor. Likewise, in any autoimmune disease, it is worth testing vitamin D levels, as these are often deficient in Hashimoto’s and can contribute to a less efficient immune system. 

Overall, there are many more blood tests that can give us a snapshot of overall health in those who suffer from thyroid disorders. However, it is best to go into more specifics with an endocrinologist and/or functional medicine doctor. However, these basics that we have spoken about are an excellent comprehensive start.