Thyroid Stimulating Hormone (TSH) Testing

What is the Thyroid Gland?

The thyroid is a butterfly-shaped gland located near your Adam's apple that produces the hormones triiodothyronine (T3) and thyroxine (T4). T3 and T4 regulate all aspects of your metabolism, such as maintaining the rate that your body uses carbohydrates, helping to control your body temperature, and regulating protein production.

What Is TSH?

Thyroid stimulating hormone (TSH) is a hormone produced by the pituitary gland at the base of the brain that helps to control thyroid activity. TSH stimulates the thyroid gland to produce the hormone thyroxine (T4) and its more bioactive form, triiodothyronine (T3). These two hormones influence many body processes, particularly metabolism.

tsh testing

TSH levels fluctuate if the production of T4 and T3 slows or accelerates: If T3 and T4 levels are high, less TSH is produced, and if T3 and T4 levels are low, more TSH is produced. Elevated TSH levels are often indicative of an underactive thyroid, a condition known as hypothyroidism. Conversely, low TSH levels may indicate too much T4 output in the blood which occurs when the thyroid gland is hyperactive, as with hyperthyroidism.

The mainstream medical model relies heavily on TSH levels to assess thyroid function; according to the conventional model, if your thyroid is working properly, TSH levels in your blood will be balanced, or within range. However, your thyroid may not be functioning properly, even if your TSH levels are normal. It important to evaluate additional thyroid biomarkers in your lab testing, in order to get the complete picture.

When applied correctly and used with additional thyroid hormone evaluations and a thorough discussion of symptoms, testing TSH levels in the blood can be a useful tool to help accurately assess thyroid function.

What Causes TSH Levels to Fluctuate?

Thyroid hormones are required for healthy metabolic function in every cell of the body. Therefore, maintaining thyroid health is crucial, as a deficiency of thyroid hormones can affect virtually all bodily functions. Many factors can affect healthy thyroid function, resulting in fluctuating levels of TSH to compensate for thyroid hormone imbalances, including:

  • Stress
  • Pregnancy
  • Medications such as birth control pills and hormone replacement therapy
  • Inflammation
  • Oxidative stress (low levels of antioxidants)
  • Autoimmune conditions

Toxins such as pesticides, mercury, lead, fluoride, and bromide can negatively impact the thyroid gland and thyroid hormone synthesis. Several nutrients are also required to properly synthesize thyroid hormones and a deficiency of specific vitamins or minerals including iodine, selenium, iron, vitamin A, vitamin D, and zinc can significantly disrupt thyroid hormone synthesis.

TSH Testing Options

Traditional Thyroid Testing

In conventional medicine settings, blood testing of TSH levels is the first and often only step a physician may take if you experience signs or symptoms of an underactive or overactive thyroid. However, TSH testing alone is an incomplete way of assessing thyroid function and could lead to undiagnosed thyroid disease or mistreatment.

One of the primary reasons TSH testing is not the most effective means to evaluate thyroid health is the wide reference range that is used to assess whether your TSH levels are "normal." The wide bell curve that is reported by conventional standards (0.5-4.5) is only helpful for diagnosing severe cases of hypothyroidism, which would be indicated by extremely elevated levels of TSH. On the other hand, very low levels of TSH would indicate severe hyperthyroidism. However, there are many people that suffer from thyroid dysfunction that would go unnoticed if we had to rely on this methodology Research studies that have thoroughly investigated TSH levels by testing subjects that did not have diseases or factors known to affect thyroid function have reported that TSH in healthy individuals fall in the range between 0.3 to 2.5. The National Academy of Clinical Biochemistry (NACB) in 2002 recommended that the upper limit of the reference range for TSH be lowered since the current standard range does not represent what is optional functioning within the thyroid system. Since then, functional medicine practitioners evaluate TSH levels with a much smaller range--it is important to 'fine tune' levels of TSH and test additional thyroid hormone levels, along with thorough investigation of symptoms, in order to properly investigate thyroid dysfunction.

Comprehensive Thyroid Testing: Testing Free T3 and Reverse T3 Levels

In order to have a thorough assessment of your hormones, a complete thyroid panel, which includes testing for blood levels of TSH, free T4, free T3 and RT3 and thyroid antibody testing, should be included in your laboratory evaluation. Of those levels, your free T3 level--T3 not bound to proteins--is the most indicative of thyroid disease, if the reference range is not within healthy standards.

comprehensive thyroid testing

While both T3 and T4 play a role in metabolic processes, T3 is five times more biologically active than T4. T3 binds to receptors on your cells and, when at adequate levels, free T3 makes you feel energized and well.

The hormone reverse T3 (RT3) should also be included in your lab testing panel. RT3 is converted from T4. However, unlike T3, it is not a hormone that produces positive health results. RT3 binds to thyroid hormone receptors and blocks T3 from doing its job. Elevated RT3 levels can inhibit proper thyroid hormone responses in cells, even if T3 levels are found to be within the normal range. Many factors can lead to elevated levels of RT3 such as high levels of stress, inflammation, toxins and oxidative stress, or low antioxidant levels in the body.

Understanding Thyroid Hormone Reference Ranges

Your thyroid panel will provide much more insight as to the way your thyroid is functioning and whether any imbalances are interfering with cellular signaling and your body's metabolism. It is important that the full clinical picture is evaluated, along with optimal ranges for TSH evaluation, so that none of the important clinical factors are missed and to be sure that your thyroid if truly functioning at its best.

The conventional reference ranges for thyroid blood testing often include the following ranges which are considered to be "normal":

  • TSH between 0.5 to 4.5
  • RT3 between 10-24
  • Free T3 between 2.3 to 4.2

Using these optimal ranges can lead to a much more thorough evaluation of your thyroid hormone status and can be a much more accurate gauge to prescribe thyroid hormone replacement therapy if necessary.

Optimize Your Thyroid Function

A thorough evaluation of your medical history, symptoms, and comprehensive thyroid testing can help determine whether the symptoms you are experiencing are due to a thyroid imbalance. If a thyroid imbalance is present, there are several treatment options available to help optimize thyroid levels, such as desiccated thyroid medication.

To find a doctor in your area that can evaluate your thyroid levels, click here.


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