9 Thyroid Tests Essential To Evaluating Thyroid Function 

By  Dr. Luke Martin, D.C.

The thyroid gland, although small, is crucial to the regulation of metabolism and energy through the release of hormones. Like all functions in the body, the thyroid gland is part of a system (specifically, the endocrine system). As with any system, a break down in any part of the system can result in sub-optimal performance of the system. With the thyroid system, this can manifest with symptoms such as:

  • Fatigue, even after a good night’s sleep
  • Weight gain
  • Difficulty losing weight, even with restrictive diets and intense exercise.
  • Mood swings
  • Sensitivity to cold weather
  • Dry skin and brittle hair/nails
  • Brain fog
  • Constipation

A poor performing thyroid system is not just about the thyroid gland, however, but about how the overall SYSTEM is performing. This is why it is so important to evaluate the thyroid SYSTEM with multiple tests, so that it can be clear as to what the root cause of the issue is. It is important to note that there can be multiple breakdowns in the system AND every person is different. Currently, the “gold standard” of thyroid testing used by the majority of healthcare practitioners is solely the test for Thyroid Stimulating Hormone (TSH). While this test can be indicative of primary hypothyroidism and hyperthyroidism, it certainly does NOT give the entire picture. In fact, it is possible (and very common) for the TSH test to show “normal” levels, yet a problem exists in another area. Because of this, many women continue to suffer for years with unresolved symptoms. Below are some of the tests that I use in my practice to understand the ENTIRE picture of thyroid performance.

TSH (Thyroid Stimulating Hormone)

What it measures: How much Thyroid hormone (T4 and T3) the pituitary gland is telling the thyroid to make.

Why it is important: When the thyroid hormone levels are low, the pituitary gland will release more TSH. When thyroid hormone levels are high, the pituitary gland will release less TSH. If the level of TSH is outside of a reference range (either too low, or too high) a diagnosis of primary hypothyroidism (TSH too high) will be made or primary hyperthyroidism (TSH too low). As mentioned prior, other thyroid markers should be run for a thorough evaluation. Additionally, there are some other issues with the TSH test ranges themselves. The test ranges given are often different lab to lab. For example, one lab may have a TSH test range that says “normal” is between 0.6 and 4.5. Another lab may have a TSH test range that says “normal” is between 0.5 and 5.0. Even with the establishment of these “normal” ranges, controversy exists in the field on what the upper and lower limits should be based on long term studies that determine the risk of developing hypothyroidism through time. Further studies have identified that individuals can have different structures of TSH molecules.

Total T4 (Total Thyroxine)

What it measures:  The amount of T4 (thyroxine - a less active thyroid hormone) bound to a protein carrier in the blood, plus free T4.

Why it is important: The majority of T4 in the bloodstream is bound to a protein carrier. In some cases, T4 cannot be released from the carrier, indicating a binding globulin problem.

Free T4 (Free Thyroxine)

What it measures:  How much T4 (thyroxine) is available to be converted into T3 (triiodothyronine - the most active thyroid hormone).

Why it is important: Only Free T4 and T3 are available to act upon tissues. While T4 is less potent than T3, in a healthy individual, there is generally more of it, and its effect lasts longer. A normal TSH level along with low free T4 could indicate an issue with either the pituitary gland, hypothalamus, or the thyroid gland.

Total T3 (Total Triiodothyronine)

What it measures:  Includes the amount of T3 bound to a protein carrier in the blood, plus free T3.

Why it is important: Once T4 is converted to T3, it is also carried into the bloodstream by a protein carrier. Like T4, sometimes T3 cannot be released from the carrier, indicating a binding globulin problem.

Free T3 (Free Triiodothyronine)

What it measures:  How much of this hormone is available for ENERGY and METABOLISM.

Why it is important: Free T3 is the more potent of the thyroid hormones available for metabolism. However, the thyroid gland makes very little T3, therefore T4 must be converted into T3. When free T3 is low, and free T4 is normal, this indicates an under conversion issue.

Reverse T3 (rT3)

What it measures:  An inactive form of T3 that can be converted from T4.

Why it is important: This hormone can block the effect of T4 and T3. The body will convert excess T4 into rT3 when it feels it needs to conserve energy, or in times of stress. When free T3 is low, and rT3 is elevated, symptoms of hypothyroidism will manifest.

T3U - T3 Uptake

What it measures:  This test indicates how the proteins that carry the thyroid hormones are binding with the hormones.

Why it is important: Most of the thyroid hormone circulating in the body is bound to thyroid binding globulins. When there is excess TBG, T3 uptake will be lower, and conversely, when there is less, T3 uptake will be higher. Other hormones in the body (estrogen and testosterone) can influence the amount of TBG.

Free T4 Index (FTI)

What it measures:  Used to estimate the amount of Free T4 circulating in the bloodstream, using Total T4 and T3U results.
Why it is important: Simply another way to measure Free T4.

TPO and Anti-TG Antibodies (TPOab and TGab)

What it measures:   Indicates if an autoimmune disease is attacking the thyroid.

Why it is important: These tests are for autoimmune thyroid disease. Roughly 90% of hypothyroidism/hyperthyroidism cases in the United States are due to autoimmune disorders (either Hashimotos or Graves); these tests are absolutely CRITICAL.

The entirety of these tests helps give a better understanding of what is happening with the entire system. In my practice, we use these tests, and actually, quite a bit more to fully understand the root cause of the thyroid issue. Symptoms, lifestyle, and personal history are also important pieces to understanding the hypothyroid puzzle. The good news is that with the right care, living with hypothyroid symptoms does not have to be part of someone’s life. Using an individualized approach that focuses on discovering root causes, we’ve been able to help many women regain their energy and lives.

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