Understanding Thyroid Labs
Anyone who struggles with thyroid function knows that it’s all too common for their labs to look “fine” and yet still feel tired all the time or have mood swings, brain fog, constipation, hair loss, or other concerns.
That’s why in functional medicine, we also:
✔️ Monitor more than just TSH
✔️ Optimize nutrition for thyroid hormone synthesis
✔️ Support conversion of T4 to the more active T3
✔️ Calm inflammation & oxidative stress
✔️ Identify & address root causes (metals, toxins, nutrient deficiencies, infections, stress, etc.)
First, let’ understand how to read thyroid lab results
To accurately assess thyroid function, a comprehensive panel of thyroid tests is essential. Each of these tests provides specific insights into various aspects of thyroid health. In this article, we'll break down what each thyroid lab value means and discuss the optimal ranges for these values.
Thyroid Peroxidase Antibody (TPO)
What it is: TPO antibodies are markers of autoimmune thyroid disease. Thyroid peroxidase is an enzyme essential for thyroid hormone production. When the immune system attacks this enzyme, it can lead to conditions like Hashimoto's thyroiditis or Graves' disease.
Optimal Range: Negative to low positive. Ideally, TPO antibodies should be as low as possible, preferably under 9 IU/mL. Elevated levels indicate autoimmune activity against the thyroid.
Thyroglobulin Antibody (Tg Ab)
What it is: Tg antibodies target thyroglobulin, a protein produced by the thyroid gland. Elevated Tg antibodies are another indicator of autoimmune thyroid disease.
Optimal Range: Negative to low positive. Optimal levels should be less than 4 IU/mL. Higher levels suggest autoimmune activity.
Total T3 (Triiodothyronine) and Total T4 (Thyroxine)
What they are: Total T3 and T4 measure the total amount of thyroid hormones in the blood, including those bound to proteins. These tests provide a broad view of thyroid hormone production.
Optimal Ranges:
Total T3: 100-200 ng/dL
Total T4: 5-12 µg/dL
Total T3 and T4 levels outside these ranges may indicate thyroid dysfunction, but they don’t provide the complete picture.
Free T3 (Free Triiodothyronine) and Free T4 (Free Thyroxine)
What they are: Free T3 and Free T4 measure the unbound, active forms of thyroid hormones available to the body’s cells. These tests are more accurate indicators of thyroid function than total hormone levels.
Optimal Ranges:
Free T3: 3.2-4.4 pg/mL
Free T4: 1.0-1.5 ng/dL
Optimal levels of free T3 and T4 ensure that the body has enough active thyroid hormone to maintain metabolic balance.
Reverse T3 (rT3)
What it is: Reverse T3 is an inactive form of T3. It is produced in response to stress and illness and can block the action of active T3. High levels of reverse T3 can contribute to hypothyroid symptoms despite normal TSH, T3, and T4 levels.
Optimal Range: 10-24 ng/dL. Lower levels within the range are preferable to ensure that reverse T3 is not inhibiting the action of free T3.
Thyroid-Stimulating Hormone (TSH)
What it is: TSH is produced by the pituitary gland and regulates thyroid hormone production. It’s often used as the primary screening test for thyroid function, but it doesn’t provide a complete picture on its own.
Optimal Range: 0.5-2.5 mIU/L. While the conventional range is typically broader (0.5-4.5 mIU/L), an optimal TSH level closer to 1.0-2.0 mIU/L is ideal for most people, indicating balanced thyroid function.
Thyroid-Stimulating Immunoglobulin (TSI)
What it is: TSI antibodies are markers of Graves' disease, an autoimmune disorder that causes hyperthyroidism. TSI antibodies stimulate the thyroid gland to produce excess thyroid hormones.
Optimal Range: Negative to low positive. Optimal levels are typically less than 1.3 IU/L. Elevated TSI levels indicate active Graves' disease.
Interpreting Thyroid Labs Holistically
When interpreting thyroid labs, it's crucial to consider all values collectively rather than in isolation. Part of the picture is also comparing the lab values to the symptoms or flags that your body is displaying.
Your body is more than just numerical values.
Looking beyond the thyroid labs, we also want to assess hormones, cortisol and adrenal/stress markers, key nutrients, and immune function for a fully comprehensive workup.
Why? This is because rarely is a thyroid problem JUST a thyroid problem.
As we have been discussing in our recent blogs, the thyroid is part of the larger endocrine system - which includes hormones produced in the brain, adrenals ovaries, and pancreas too. Hormones that have a bidirectional relationship with the thyroid include cortisol (stress hormone), insulin (blood sugar regulation), and estrogen (reproduction).
This is why we take a whole-person approach!
If you are looking for a whole-body approach to thyroid health, fill out our short online application and our clinical liaison will follow up with you about how we can help your unique thyroid health.
