What Are Optimal Thyroid Levels, and How Do You Achieve Them?

optimal thyroid levels: Thyroid level meter at the maximum level

When you see your first set of thyroid panel test results, you may feel like you’re trying to decipher a bowl of alphabet soup. It’s important to know these two important measurements to understand your thyroid test results:

  • Standard thyroid levels: This is the reference range labs use to diagnose thyroid conditions. If your blood test results fall outside the normal lab ranges, you may have a thyroid condition.
  • Optimal thyroid levels: These are considered when treating and managing your thyroid condition. Optimal thyroid levels are condition-specific and give you a target range for aim for.

In this article, we’ll discuss standard vs. optimal reference ranges and steps you can take to achieve optimal thyroid levels. 

Standard and Optimal Thyroid Reference Ranges

optimal thyroid levels: Thyroid panel reference guide chart by Dr. Ruscio

Standard reference ranges are the normal range of test results that are expected in healthy individuals. Test results that fall outside of these ranges indicate a thyroid disease or thyroid dysfunction.

For those already diagnosed and in treatment for a thyroid condition, keep optimal thyroid levels in mind when adjusting medication and monitoring your progress.


Thyroid-stimulating hormone, or TSH, is produced in the pituitary gland. As the name suggests, the role of this hormone is to stimulate the thyroid gland to produce thyroid hormones (T4 and T3). TSH increases when your body’s thyroid hormone levels are low and decreases when levels are high. This makes TSH testing an excellent indicator for hypothyroid (low TSH) and hyperthyroid (high TSH) conditions.

The standard reference range for normal TSH is 0.45−4.5 IU/mL1. Standard ranges may need to be adjusted if you are over 60 years of age or pregnant.

Aim for optimal TSH levels of 2.5-0.45 IU/mL2 if you are hypothyroid and taking thyroid hormone replacement.

Free T4

Thyroxine, or T4, is a thyroid hormone made by the thyroid gland. T4 regulates several body functions including, metabolism, energy production, and body temperature. 

T4 can be measured in different ways:

  • Free T4: Available T4 hormone that bodily tissues can use. This is the active form of T4 and most accurate test for thyroid function.
  • Bound T4: T4 hormone that binds to protein and can’t be used by bodily tissues Approximately 99.8% of T4 hormone is bound T4 
  • Total T4: Measures bound T4 and Free T4

The standard reference range for free T4 is 0.82-1.77 ng/dl.

Aim for optimal Free T4 levels of 1.3-1.77 ng/dl if you are hypothyroid and taking thyroid hormone replacement.

Free T3

Triiodothyronine, or T3, is also produced by the thyroid gland but in smaller amounts than T4. 

Though it can be included in a thyroid panel, Free T3 is not an accurate measurement for thyroid conditions. Low Free T3 usually indicates digestive problems, high levels of inflammation, high stress, poor sleep, and/or eating too few carbs or calories.

The standard reference range for free T3 is 2.0−4.4 pg/mL

Aim for optimal Free T3 levels above 3 pg/mL if you are hypothyroid and taking thyroid hormone replacement.

Lifestyle improvements, treatment of gut imbalances, and resolving nutritional deficiencies are generally the best approaches for treating low T3. While some practitioners prescribe T3 hormone replacement, this does not address the root cause of low T3. Excess T3 medication can cause adverse reactions for some patients.

Thyroid Antibodies

Thyroid antibodies become elevated when you have an autoimmune disease such as Hashimoto’s thyroiditis or Grave’s disease. Thyroid function tests on a thyroid panel usually include TPO antibodies and TG antibodies.

TPO (thyroid peroxidase antibodies) provides the most accurate marker of Hashimoto’s disease and autoimmune thyroid conditions3. Positive TPO levels indicate autoimmune thyroid activity and likely inflammation of the thyroid gland. 

The standard reference range for TPO considers levels above 35 IU/mL to be positive for thyroid autoimmunity. However, positive TPO does not mean you are or will become hypothyroid or hyperthyroid. 

  • TPO levels between 35 and 500 IU/mL indicate a slight risk of progression to hyperthyroidism or hypothyroidism4.
  • TPO levels over 500 IU/mL indicate a moderate risk of progression to hypothyroidism5. 

Aim to reduce TPO levels below 500 IU/mL if they are higher than this. This can generally be achieved through lifestyle changes and treatment of gut conditions. For patients with Hashimoto’s disease, reducing TPO levels below 35 is unnecessary.

TG (thyroglobulin antibodies) levels may be included in antibody testing. However, they are not an accurate predictor of autoimmunity3.

The standard reference range for TG considers levels above 0.9 IU/mL to be positive for thyroid antibodies. TG levels over 9 IU/mL may suggest the risk of progression to hypothyroid. However, research data is not conclusive6.

2 Ways to Achieve Optimal Thyroid Levels

optimal thyroid levels: Thyroid gland model and a stethoscope on a table

Now that we’ve discussed the finer points of thyroid lab reference ranges, let’s take a look at two ways you can achieve optimal thyroid levels. 

Thyroid Medication

The first step in achieving optimal thyroid levels is taking a thyroid medication, such as levothyroxine, to normalize thyroid hormone levels. As discussed earlier, aim for the following optimal thyroid levels:

  • TSH levels: 2.5-0.45 IU/mL
  • Free T4 levels: 1.3-1.77 ng/dl

Achieving optimal thyroid hormone levels with thyroid hormone replacement medication can eliminate thyroid symptoms like constipation, poor mood, weight gain, fatigue, and brain fog. 

However, if symptoms continue after you optimize thyroid hormone levels, we need to dig deeper. Lingering symptoms despite adequate thyroid hormone medication generally signal underlying gut conditions, which have symptoms that are very similar to hypothyroidism.

Improve Gut Health

Thyroid symptoms vs gut symptoms chart by Dr. Ruscio

Thyroid hormone replacement won’t resolve your symptoms if gut imbalances like dysbiosis, leaky gut, and gut inflammation are the real root causes. Improving your gut health can help to: 

  • Resolve stubborn symptoms that may not be caused by your thyroid
  • Reduce thyroid inflammation
  • Lower thyroid antibodies
  • Increase T3 levels 
  • Improve absorption of thyroid hormone replacement medication

The strong connection between gut health and thyroid problems is supported by a significant body of research that shows:

  • Thyroid conditions and gut conditions commonly occur in the same patients 7 8 9 10 11.
  • Improving gut health can improve thyroid health 12 13 14 15 16 17 18.
  • Symptoms found in thyroid disorders (depression, brain fog, headache, anxiety, and fatigue) are common symptoms of gut disorders 8 19 20 21 22. 

To learn more about steps you can take to improve gut health, check out our Gut Health 101 guide.

Bottom Line

Standard lab values for thyroid tests are important for diagnosing thyroid conditions. During treatment, however, it can be helpful to adjust your focus and shoot for optimal levels which may be different from standard lab ranges.

Optimal levels of TSH and T4 can be achieved easily by adjusting thyroid hormone medication dosage. Optimizing T3 and TPO levels, however, is not a quick fix and requires attention to lifestyle improvements and treatment of gut issues.

At Austin Center for Functional Medicine, we encourage thyroid patients to focus on natural healthcare approaches that improve gut health, decrease systemic inflammation, and support immune system health, while also optimizing thyroid hormone medication.

Contact us today for more information on improving your thyroid health.


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