The Thyroid Function Tests You Need To Know About

The Thyroid Function Tests You Need To Know About

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Human Thyroid Gland

Thyroid hormone is so important that without enough of it, it’s virtually impossible to maintain the balance and production of all other hormones. Adequate production of thyroid hormone is required to make necessary amounts of growth hormone, progesterone, DHEA, testosterone, estrogen, cortisol, insulin, brain neurotransmitters, and many others.

The reality is that all these hormones work in concert, and the thyroid is a critical part of the symphony. But how do you know if you’re producing too much or too little thyroid hormone?

Photo of a student sleeping on a pile of books

Thyroid Symptoms

Often, poor thyroid function is accompanied by very common, tell-tale symptoms. However, the difficulty is that the symptoms tend to overlap with other conditions that may not be directly related.

Symptoms associated with underactive (hypo) thyroid function typically include some or all of the following: fatigue, weight gain, inability to lose weight, dry skin, poor digestion, hair loss, brittle nails, cold hands and feet, lack of energy, tendency to bruise easily, depression, change in menstrual cycle, memory problems, and loss of hair on the outer third of your eyebrows.

Hypothyroidism is the most common form of thyroid dysfunction. Although less common, hyperthyroidism (overproduction of thyroid hormone) is just as serious and may include some of the same symptoms as hypothyroidism. Common symptoms of an overactive thyroid tend to include rapid or irregular heartbeat, inability to gain weight, protruding or bulging eyes, irregular or no menstrual cycle, inability to concentrate, nervousness, irritability, difficulty sleeping, increased sweating, and tremors, among others.

Photo of a Thyroid Examination

Assessing Thyroid Function

In order to confirm a thyroid condition, analysis and diagnostics must be performed. Methods of determining thyroid function include physical examination, basal body temperature, and laboratory testing. Measuring your body temperature in the morning is a simple and sometimes imprecise method of checking thyroid function.

While this method can be used to help identify a dysfunctional thyroid, it may not be extremely useful in determining how or why the thyroid isn’t working well or if the problem is truly occurring in the thyroid.

Another investigative method is physical examination—looking at and feeling the thyroid. This method can be used to identify the presence of nodules, which may need to be looked at via ultrasound. Again, the limitation of this method is the inability to identify thyroid hormone production and how your cells are using it.

Blood testing is really the primary way to know how well the thyroid is performing. While blood test results represent only a snapshot in time and will change throughout the day, week, or a woman’s cycle, the results tend to be a very good reflection of how the thyroid is operating.

Unfortunately, many doctors include only a few markers of thyroid production on routine work-ups. Most commonly, you’ll only see TSH. If you’re lucky, T3 and T4 will also be included in your blood test. It’s rare that insurance will cover any other thyroid-specific markers. But thyroid function is more complicated than that.

Illustration of TSH panel

Full Thyroid Panel

TSH stands for thyroid-stimulating hormone. This is a hormone produced by the pituitary gland in the brain that gets sent to the thyroid, telling it to produce hormones. So TSH really isn’t even a thyroid hormone, it’s a brain hormone—and yet it’s usually the only thyroid-related marker included in blood draws.

To get a full picture of thyroid function, there are a number of other thyroid-specific markers that must be run on your blood test. A full thyroid panel should include TSH, total T4 (thyroxine), total T3 (triiodothyronine), free T3, reverse T3 (rT3), thyroid binding globulin (TBG), thyroglobulin antibodies (Tg Ab), and thyroid peroxidase antibodies (TPO Ab). If hyperthyroidism is suspected, you should test for TSI antibodies as well. T3 uptake is another marker that can be included in addition to or in place of TBG.

Illustration of thyroid gland function

Understanding Your Test

TSH: A hormone produced by the pituitary gland that tells the thyroid to produce thyroid hormones.

T4: Produced directly by the thyroid gland. Inactive form of thyroid hormone. Includes free T4 and bound T4. Approximately 93% of the hormones produced by thyroid gland are in this form.

T3: Active form of thyroid hormone. Includes free T3 and bound T3 and accounts for about 7% of what the thyroid produces. Additional T3 must then be made by converting T4 to T3 in the liver, gastrointestinal tract, and peripheral tissues.

Free T3: Free fraction of total T3. Only free T3 is available for binding to cell receptor sites so that it can be used.

rT3: Made in the liver by converting from T4. Available for binding to cell receptor sites but doesn’t result in cellular activity.

Photo of blood tube saying Thyroid panel on a label

TBG: Protein made in the liver that acts as a taxi cab for moving thyroid hormones throughout the bloodstream. Renders thyroid hormones bio-unavailable until they reach their destination.

T3 Uptake: Percentage of T3 hormone that’s successfully taken up by cell receptor sites.

Tg Ab: Autoantibodies produced by the immune system that target thyroid tissue for destruction.

TPO Ab: Autoantibodies produced by the immune system that target both thyroid and cerebellar (brain) tissue.

TSI Ab: Autoantibodies produced by the immune system that target thyroid receptors and can lead to the overproduction of thyroid hormones.

Illustration of human Endocrine System

Thyroid Physiology

Thyroid physiology can be quite complex. If you or your practitioner suspects a dysfunction related to your thyroid, it’s paramount that all the previously listed markers are included in your blood test. From there, an experienced practitioner can determine where things are going wrong.

These markers will help you understand if your issues are upstream at the brain level, if they’re occurring in the thyroid itself, if there are issues downstream of the thyroid where conversion and uptake occurs, or if the immune system is attacking the thyroid. When you can determine where in the dysfunction is occurring, you can begin to identify the underlying contributing factors.

Photo of a board with Hashimoto disease written on it

Contributors to Thyroid Dysfunction

In general, a vast majority of thyroid-related issues don’t actually occur in the thyroid. Mostly commonly, the problem can be traced back to circadian rhythm disruptions that result in pituitary dysfunction and poor thyroid feedback controls.

Additional common contributors to thyroid dysfunction are inflammation and excess stress, as these can directly inhibit thyroid hormone production, as well as conversion from T4 to T3. Intestinal permeability, dysbiosis, and impaired liver function can also play a role in under-conversion of T4 to bioavailable T3.

Interestingly, 20-30% of those with Hashimoto’s never test positive for elevated antibodies. In this case, an ultrasound may be useful to confirm diagnosis. Because thyroid physiology is extremely interactive with a number of systems in the body, a functional or integrative practitioner can help you truly understand where dysfunction is occurring and how it may be interacting with thyroid hormone production.