What Are Considered Normal Thyroid Hormone Levels?

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Your thyroid gland is an essential part of your endocrine system. It secretes hormones that regulate metabolism, heart function, digestion, muscles, brain development, and bone health.

As functional healthcare providers, we test for levels of thyroid hormones beyond just TSH. Comprehensive thyroid hormone testing allows us to identify the root cause of many thyroid problems, not just the most severe cases.

In this article, we’ll talk about typical thyroid hormone levels, important tests, and what to do if you have hypothyroidism.

What Are Thyroid Hormones?

Thyroid hormones are secreted by the thyroid gland — the butterfly-shaped gland at the base of your neck. 

There are 3 thyroid hormones, but T4 and T3 are the most prominent. TSH, which is not actually made by the thyroid, is also a hormone vital to thyroid function, which is often what providers refer to when they mention “thyroid hormones.”

Here’s how each thyroid hormone functions within the body:

  • T4 (thyroxine): The primary hormone produced by the thyroid gland. Also known as tetraiodothyronine, T4 is considered inactive. Its primary function is to become active T3.
  • T3 (triiodothyronine): The active form of T4. It regulates your metabolism and other vital functions. Just 20% of T4 is produced in the thyroid. Most T3 is produced from T4 in other organs (like the kidneys and liver).
  • Calcitonin: The less prominent hormone that your thyroid gland produces. It helps regulate calcium and phosphate levels in your blood, contributing to healthy bones.
  • Thyroid-stimulating hormone (TSH): The production of thyroid hormone TSH occurs in the pituitary gland and stimulates the creation of T3 and T4. This is the hormone most often assessed for thyroid function.
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How We Assess Thyroid Hormone Levels

Many conventional primary care doctors and endocrinologists focus primarily on TSH levels. As functional healthcare providers, we administer a more robust set of thyroid function tests than most of the medical community.

Additionally, it’s important to consider optimal levels versus reference ranges. That’s why we administer a more thorough panel of tests to hypothyroid patients.

It’s important to remember that if you’re taking thyroid medications, the time from your last dose will change how we interpret your lab values. Your provider may have you test your thyroid panel before or after taking your medication in the morning to assess your thyroid levels at various times during the day.

We believe the most accurate and thorough way to test for thyroid function is to measure:

  • TSH levels
  • Free T4
  • Free T3
  • Total T4
  • Total T3
  • Reverse T3
  • Anti-thyroglobulin and anti-TPO antibodies (Hashimoto’s thyroid antibodies)
  • Thyroid-binding globulin (TBG levels)

Important: Make sure you’re not taking biotin (vitamin B7) when testing for thyroid hormone levels. This popular supplement for hair and nail growth can interfere with test results.

TSH Levels

Optimal TSH hormone levels are 0.5-5.0 mIU/L, according to the mainstream medical community. But based on the best available research, we recommend 0.5-2.5 mIU/L — especially for pregnant women — for optimal thyroid function.

Pregnancy tends to reduce TSH values. You may dip below 0.5 mIU/L but remain euthyroid (which means your thyroid is healthy). Thyroid hormone levels may rise with each trimester, and then spike postpartum, but this is perfectly normal in the short term.

TSH Test

Testing levels of TSH is a common and critical part of any health practitioner diagnosing thyroid disorders. A blood test is the typical way to assess TSH levels.

The American Thyroid Association recommends serum TSH levels stay 0.4-4.0 mIU/L (milli-international units per liter). We recommend keeping that number even lower — below 2.5 mIU/L.

However, we recommend keeping TSH levels between 0.5 and  2.5 mIU/L. If your TSH levels are too high, you may be hypothyroid. If your thyroid levels are too low, you may be hyperthyroid.

Certain medications might interfere with TSH measurements, like:

  • Amiodarone
  • Dopamine
  • Lithium
  • Potassium iodide
  • Steroids like prednisone

What are normal TSH test results for thyroid levels? 

The normal range of thyroid test results is 0.5-5.0 mIU/L, but we recommend TSH levels stay under 2.5 mIU/L. If your TSH level sits outside this reference range, you probably suffer from a thyroid disorder that needs to be treated.

What is a normal TSH level in a woman? 

An optimal TSH level in a woman is 0.4-2.5 mIU/L. For pregnant women, that upper limit is stricter than if you are not pregnant.

A dangerously high level of TSH is above 10.0 mIU/L. High TSH means low thyroid hormones. This could indicate severe hypothyroidism.

What is considered a low thyroid level? 

A TSH level below 0.4 is very low, possibly indicative of hyperthyroidism (an overactive thyroid).

High vs. Low TSH

High TSH levels mean that you have primary hypothyroidism or subclinical hypothyroidism. Low TSH levels either mean that the pituitary gland is not functioning and you could have secondary hypothyroidism, or that you have hyperthyroidism (most likely from Grave’s disease).

Neither high nor low TSH is less of a problem than the other; both need to be addressed.

There are two main forms of hypothyroidism (an underactive thyroid):

  1. Primary hypothyroidism: Primary hypothyroidism is when your thyroid itself is the reason your body isn’t making enough thyroid hormone. There’s not another part of your body triggering thyroid dysfunction.
  2. Secondary hypothyroidism: If you produce too little TSH, you could suffer from secondary hypothyroidism, which means your thyroid disorder is caused by dysfunction wit the pituitary gland.

Another form of secondary hypothyroidism, or tertiary hypothyroidism, occurs when your hypothalamus releases too little thyrotropin. This issue with the hypothalamus can affect the pituitary gland, which in turn affects the thyroid gland.

What may be causing high TSH? Autoimmune diseases such as Hashimoto’s, toxin exposure, or even food allergies may be causing high TSH levels, which is due to low thyroid hormone levels and hypothyroidism.

What may be causing low TSH? Common causes of low TSH levels include:

  • Autoimmune diseases
  • Thyroid nodules
  • Inflammation
  • Inactive or underactive pituitary or hypothalamus glands
  • Medication side effects

T4 Levels

Testing free T4 levels is standard practice for some medical practitioners. We also test total T4 for a complete picture. Both of these are blood tests. 

Our goal during treatment is to optimize our patient’s thyroid hormone levels to be in the middle-to-upper end of these thyroid hormone ranges (for free and total T4 and T3).

Typical T4 levels should be:

  • Total T4 = 0.4-2.5 mIU/L or 5,000-12,000 ng/dL (nanograms per deciliter of blood)
  • Free T4 = 0.9-1.9 ng/dL

T3 Levels

Many healthcare professionals don’t test for T3 levels and rely primarily on TSH and T4 tests. We believe testing T3 levels is crucial to understanding a fuller picture of your thyroid function.

We test the following T3 levels: total T3, free T3, and reverse T3. These all can be measured via a blood test.

Typical T3 levels should be:

  • Total T3 = 75-195 ng/dL (nanograms per deciliter of blood)
  • Free T3 = 2.3 – 4.2  pg/dL
  • Reverse T3 = 10-24 ng/dL
  • Optimal reverse T3 levels would be around 15. Higher values are indicative of inflammation or stress (mental or physical).

T3 (triiodothyronine) impacts heart rate and the way your heart functions.

Symptoms of a Thyroid Issue

Hyperthyroidism and hypothyroidism are thyroid diseases caused by unbalanced thyroid levels. Thyroid replacement therapy often treats the following symptoms without actually addressing the root issue that’s causing the disease in the first place.

Thyroid disease symptoms include:

  • Enlarged thyroid (goiter)
  • Exhaustion
  • Weight gain or weight loss
  • Muscle and joint pain
  • Dry skin
  • Thinning hair or nails
  • Temperature intolerance
  • Digestive problems
  • Depression and other mood disorders
  • Irregular heartbeat
  • Swelling
  • Eye problems

Graves’ disease (hyperthyroidism) or Hashimoto’s thyroiditis (hypothyroidism) can lead to dangerously high or dangerously low thyroid hormone levels, respectively. There are many triggers for Graves’ or Hashimoto’s.

When Is Treatment Needed?

Treatment is needed when your thyroid levels are too high or too low, ranging outside the optimal levels. Normal TSH levels are typically considered 0.5-5.0 mIU/L. We prefer the upper limit to be 2.5 mIU/L.

Thyroid hormone replacement using levothyroxine is the most common treatment for an underactive thyroid (too little thyroid hormone). Usually, thyroid medications like levothyroxine are not our first response to treating thyroid dysfunction.

Radioactive iodine, antithyroid agents, and beta-blockers are the most common treatments for an overactive thyroid.

There are many different root causes of thyroid conditions. The best treatment for either hypothyroidism or hyperthyroidism is addressing your unique root cause, such as stress, leaky gut syndrome, toxin exposure, nutrient deficiencies, inflammatory diet, or thyroid cancer.

Here at PrimeHealth, we do just that — create individual, integrative treatments that impact the root cause of your thyroid levels.


What can happen if the TSH level is too high?

If a TSH level is too high, it may be a sign of hypothyroidism. Here are some of the symptoms of hypothyroidism:

  • Enlarged thyroid (goiter)
  • Fatigue
  • Weight gain
  • Muscle and joint pain
  • Hoarse voice, snoring
  • Dry skin
  • Thinning hair
  • Brittle nails
  • Cold intolerance
  • Constipation
  • Depression
  • Heart disease
  • Myxedema coma

 What does a low TSH mean?

A low TSH level means you either suffer from secondary hypothyroidism or hyperthyroidism. This means your thyroid gland is making too much thyroid hormone.

The symptoms of hyperthyroidism include:

  • Muscle weakness
  • Too much energy
  • Insomnia
  • Fatigue
  • Heat sensitivity
  • Diarrhea
  • Frequent urination
  • Thirst
  • Itchiness
  • Anxiety
  • Mood swings
  • Osteoporosis

Can Ayurvedic medicine effectively treat thyroid disorders?

Ayurvedic medicine may offer supportive treatment for thyroid disorders through dietary recommendations, herbal supplements, and lifestyle changes aimed at balancing the body’s energies. 

However, it’s essential to consult healthcare professionals and consider it as a complementary approach alongside conventional treatments.

Thyroid questions? Let us answer them.

Now you know all about normal thyroid hormone levels and when to seek help from a healthcare provider.

PrimeHealth is devoted to answering people’s questions about medical conditions and autoimmune diseases like Hashimoto’s thyroiditis. We believe it’s important to make patients feel heard and educated on what is going on in their bodies.

Many thyroid diseases can be permanently reversed. Even what conventional endocrinology specialists might call “permanent hypothyroidism” may be treatable. If you’re in Colorado, we’d love to help you find your cure. 


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  3. Udovcic, M., Pena, R. H., Patham, B., Tabatabai, L., & Kansara, A. (2017). Hypothyroidism and the heart. Methodist DeBakey cardiovascular journal, 13(2), 55.
  4. Delitala, A. P., Scuteri, A., & Doria, C. (2020). Thyroid hormone diseases and osteoporosis. Journal of clinical medicine, 9(4), 1034.
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