How to Interpret Your Thyroid Levels

thyroid tests, TSH, T3, T4, TPO, TSI, thyroid blood tests
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Blood tests for thyroid function are an important part of the process of both diagnosing thyroid disease, and treating thyroid conditions.

Here is a summary to help you have a better understanding of what your thyroid tests mean for the diagnosis and management of your thyroid condition.

General Guidelines

Some doctors of their office staff call to tell you your medical test results. You may hear "your results were fine," or "your tests were normal" as a test result.

Always ask for an actual copy of any medical test results, including thyroid tests. Particularly with thyroid blood tests, you need to know your actual levels, as well as the reference range, in order to advocate for the best possible thyroid care. 

Thyroid Stimulating Hormone (TSH)

  • Thyroid Stimulating Hormone (TSH): Let's start with your TSH. This measures a pituitary hormone that responds to changes in thyroid blood levels and is a key test for many doctors. At most labs in the U.S., the reference range is from around 0.5 to 5.5.
  • TSH Below Normal: If your TSH level is below the reference range, your doctor may determine that you are hyperthyroid (you have an overactive thyroid.)
  • TSH Above Normal: If your TSH level is above the reference range, your doctor may determine that you are hypothyroid (you have an underactive thyroid.)
  • Optimal TSH: Some integrative physicians and hormone experts believe that optimal TSH for safe relief of symptoms is 2.0 or below. Find out where your practitioner stands on this issue.
  • Important Note About the TSH Range: Some doctors believe that the TSH reference range is far too broad, and instead, consider 3.0 to be the top-end of the reference range, and that levels above 3.0 represent hypothyroidism. Find out where your doctor stands on this controversy.

Free T4/Free Thyroxine

  • Free T4/Free Thyroxine: Free T4 measures the free, unbound levels of the hormone thyroxine in your bloodstream. Thyroxine is a storage hormone, and must be converted by your body into T3 to actively work. Because your free levels of T4 represent immediately available hormone, free T4 is thought to better reflect your hormonal status than total T4.
  • Free T4 in the Reference Range:  Many doctors consider any level within the normal reference range to be evidence that the thyroid is functioning well. 
  • Elevated Free T4: Elevated Free T4 levels above the reference range may indicate hyperthyroidism.
  • Low Free T4: Low Free T4 levels below the reference range may indicate hypothyroidism.
  • Optimal Free T4: Some integrative physicians and hormone experts state that if free T4 is not in the top half of the reference range, it is not optimal. Find out where your practitioner stands on this issue.

Free T3/Free Triiodothyronine

  • Free T3/Free Triiodothyronine: Free T3 measures the free, unbound levels of the hormone triiodothyronine. T3 is the active thyroid hormone. Because your free levels of T3 represent immediately available hormone, free T3 is thought to better reflect your hormonal status than total T3.
  • Elevated Free T3: Elevated free T3 above the reference range may indicate hyperthyroidism.
  • Low Free T3: Low Free T3 levels below the reference range may indicate hypothyroidism.
  • Optimal Free T3: Some integrative physicians and hormone experts believe that if free T3 is not in the top half, or even the top 25%, of the reference range, it is not optimal. Find out where your practitioner stands on this issue.

    RT3/Reverse T3 

    Reverse T3 (RT3) -- also known as Reverse Triiodothyronine -- is a controversial test. Conventional physicians  for the most part dismiss the value of RT3 measurement in diagnosing, treating and managing hypothyroidism. Integrative physicians and those who focus on optimal hormone balance, however, consider elevated RT3 to be a key sign of an underactive or dysfunctional thyroid. Learn more about the Reverse T3 test now.

    Thyroid Antibodies Tests

    • Thyroid Peroxidase (TPO) Antibodies (TPOAb) / Antithyroid Peroxidase Antibodies:  Thyroid Peroxidase (TPO) antibodies are also known as Antithyroid Peroxidase Antibodies. (In the past, these antibodies were referred to as Antithyroid Microsomal Antibodies or Antimicrosomal Antibodies). TPO antibodies can be evidence of tissue destruction.
    • Normal TPO Antibodies: If TPO antibodies fall within the reference range, they are considered normal. This does not entirely rule out Hashimoto's disease but makes it far less likely.
    • Elevated TPO Antibodies: Elevated TPO antibodies can indicate Hashimoto's disease or other forms of thyroiditis. TPO antibodies are also detectable in as many as 85 percent of Graves' disease patients.

    TgAb/Thyroglobulin Antibodies

    If you have already been diagnosed with Graves' disease, having elevated levels of Thyroglobulin Antibodies (TgAb) means that you are more likely to eventually become hypothyroid. Thyroglobulin antibodies are positive in about 60 percent of Hashimoto's patients and 30 percent of Graves' patients.

    TSI/Thyroid-stimulating Immunoglobulins

    Thyroid-stimulating Immunoglobulins (TSI) are elevated in as many as 75 to 90% of Graves' disease patients. The higher the levels, the more active the Graves' disease is thought to be. (The absence of these antibodies does not, however, rule out Graves' disease.) Note: some people with Hashimoto's disease also have these antibodies, and this can cause periodic short term episodes of hyperthyroidism.

    For more information, read What Are Your Thyroid Tests Telling You? 

    Sources:

    Bahn, R., Burch, H, Cooper, D, et al. Hyperthyroidism and Other Causes of Thyrotoxicosis: Management Guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. Endocrine Practice. Vol 17 No. 3 May/June 2011.

    Braverman, L, Cooper D. Werner & Ingbar's The Thyroid, 10th Edition. WLL/Wolters Kluwer; 2012.

    Garber, J, ​Cobin, R, Gharib, H, et. al. "Clinical Practice Guidelines for Hypothyroidism in Adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association." Endocrine Practice. Vol 18 No. 6 November/December 2012.

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