An Overview of Thyroid Testing and Interpretation

 

TSH -- Thyroid Stimulating Hormone

  • Measures: A pituitary hormone that responds to levels of circulating thyroid hormone – mainly T4

  • Reference Range on Standard Labs: 0.5 – 5.5 µIU/mL.

  • Conventional Interpretation: 5.5 - 10 µIU/mL is "subclinical" hypothyroidism, over 10 µIU/mL is overt hypothyroidism.

  • Integrative Interpretation: Levels above 1.5 to 2.0 µIU/mL may be indicative of thyroid dysfunction. Optimal level is from 1.0 to 1.5 µIU/mL.

T4 - Thyroxine / Free Thyroxine - Free T4

  • Measures: Total T4 measures the total amount of thyroxine circulating in the bloodstream. Free T4 measures the available, unbound amount of thyroxine in the bloodstream. A healthy thyroid gland produces mainly T4 which is more of a pro-hormone as it needs to be converted into triiodothyronine (T3) in order to deliver oxygen and energy to cells.

  • Reference Range: Total T4: 4.5 - 12.5 µg/dL, Free T4: 0.8 - 1.8 ng/dL

  • Conventional Interpretation: Many conventional physicians do not test Total T4 or Free T4.  However, in some cases, along with elevated TSH, Total T4 or Free T4 levels that are below the reference range are considered evidence of hypothyroidism.

  • Integrative Interpretation: For diagnosis and treatment of hypothyroidism, levels in the top half of the reference range are considered optimal and evidence of proper thyroid function.

T3/FT3 - Triiodothyronine / Free Triiodothyronine

  • Measures: Total T3 measures the total amount of triiodothyronine circulating in the bloodstream. A healthy thyroid gland produces some triiodothyronine -- the active thyroid hormone. The rest is the result of conversion of T4 into T3

  • Reference Range: Free T3: (Triiodothyronine): 2.3- 4.2 pg/mL, Total T3: 80 -200 ng/dL

  • Conventional Interpretation: Many conventional physicians do not test Total T3 or Free T3. However, in some cases, along with elevated TSH, Total T3 or Free T3 levels below the reference range are considered evidence of hypothyroidism.

  • Integrative Interpretation: Integrative physicians usually only look at free T3. For diagnosis and treatment of hypothyroidism, levels in the top half of the reference range are considered evidence of sufficient thyroid function, and levels in the top 25th percentile of the reference range are considered optimal. In the integrative view, sub-optimal levels may warrant treatment with thyroid hormone replacement medications, or a medication that specifically includes T3.

RT3 - Reverse Triiodothyronine - Reverse T3

  • Measures: An inactive, useless form of T3 that is produced when the body is under stress.Reference Range: Typically 10-24 ng/dL

  • Conventional Interpretation: This test is rarely performed by conventional physicians, who see no value in this measurement.

  • Integrative Interpretation: Integrative physicians and those who some doctors who focus on optimal hormone balance consider elevated RT3 or an RT3/T3 ratio imbalance to be a key sign of an underactive or dysfunctional thyroid. They believe a healthy ratio is to have 20x more T3 than RT3.

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