throat image of thyroid gland

How to Understand Thyroid Levels

Medically reviewed on January 7, 2022. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.


Your thyroid gland is one of the most integral organs in your body. It controls or plays a role in countless bodily functions to ensure your overall health. Understanding your thyroid levels can be confusing, but it’s an important step in identifying potential health issues before they get worse. Learn more about how to understand thyroid levels below.


Check if your thyroid hormones are balanced from the convenience of home with the Everlywell at-home Thyroid Test.


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What Is the Thyroid?

The thyroid is surprisingly small for playing such an important role in your health. It’s a gland that is part of the body’s endocrine system. The thyroid is shaped like a small butterfly and is located at the front of your neck, wrapped around your windpipe [1].

As a gland, the thyroid nodule produces and secretes chemicals known as thyroid hormones. Maintaining a proper balance of hormones is essential to your health. Too much thyroid hormone can result in hyperthyroidism, while too little from an underactive thyroid can result in hypothyroidism. Both are serious health conditions that can have a major impact on your health and quality of life [2].

Broadly, thyroid hormones control your metabolism, which is the bodily process of converting food and drink components into usable energy. Outside of metabolism, thyroid hormones also control:

  • Heart and muscle function
  • Bone maintenance
  • Brain development [2]

Understanding Thyroid Hormones

While your thyroid nodule is responsible for hormone production and distributing its hormones, the gland responsible for signaling that thyroid production is the pituitary gland. Located at the base of the brain, the pituitary gland secretes a hormone called thyroid stimulating hormone (TSH), which tells the thyroid when and how much hormone to produce. The TSH, or thyroid-stimulating hormone, levels in your blood are constantly fluctuating based on your body’s thyroid hormone needs [2].

The two hormones released by the thyroid are triiodothyronine (T3) and thyroxine (T4). The thyroid produces only about 20 percent of T3, which is the more active of the two hormones. However, enzymes in your kidneys and liver can convert T4 into T3. The other 80 percent of the thyroid’s hormone production comprises T4 [2].

The thyroid also has other hormone-producing cells known as C-cells. These cells create a hormone known as calcitonin. Calcitonin controls the levels of phosphate and calcium in the blood, which ensures the health and maintenance of your bones [2].

Testing Your Thyroid Levels

Healthcare providers can determine your thyroid’s function and your thyroid hormones levels through a variety of tests. Most of these tests require a simple blood sample.

TSH Test

TSH isn’t a thyroid hormone, so why have this thyroid test? As mentioned, TSH is the hormone produced by the pituitary gland that tells the thyroid gland to start producing and secreting its hormones. While TSH levels fluctuate, significant changes can potentially act as an early warning sign of thyroid hormone issues [3].

TSH tests may detect high TSH levels, which might indicate that your thyroid isn’t making enough hormones, which can point to the autoimmune disease of hypothyroidism. Alternatively, a low TSH level in your blood may point to your thyroid overproducing hormones leading to the autoimmune disease of hyperthyroidism [4].

In other cases, TSH itself may contribute to a thyroid issue. Low TSH levels may prevent your thyroid from knowing that it needs to make more hormones, resulting in abnormally low thyroid hormone levels [4].

Although they generally can’t be used on their own, TSH tests are often the best first step in determining your thyroid’s function. Any abnormalities in your TSH test results will then require other, more thorough thyroid hormone tests [4].

T4 Tests

While it’s not the most active of the thyroid hormones, T4 is the most plentiful thyroid hormone in the blood. Free T4 tests measure the amount of T4 that is not bound to proteins and can thus freely enter other bodily tissues. Total T4 test measures both bound and free T4 levels [3].

Total T4 levels are more prone to fluctuation, especially if you are on medication. Certain drugs and medical conditions can cause changes to thyroid hormone-binding proteins. Some can increase thyroid hormone-binding proteins, leading to a higher total T4 level, while others reduce those proteins and result in lower total T4 levels [4].

Furthermore, pregnancy can contribute to total T4 levels that are outside the normal range while still having a perfectly healthy thyroid function. For these reasons, your healthcare provider or endocrinologist may recommend free T4 tests for a more accurate assessment [4].

T3 Tests

T3 tests also come in free and total variations. However, free T3 levels generally aren’t reliable for diagnostic purposes. High total T3 levels typically point to hyperthyroidism. This makes total T3 tests important in diagnosing hyperthyroidism and determining the severity of the thyroid condition [4].

On the other hand, measuring T3 levels is less useful with the autoimmune thyroid disease of hypothyroidism. T3 levels only fall in later stages of hypothyroidism. In fact, people with severe hypothyroidism can have low free T4 levels and high TSH levels but completely normal T3 levels [3].

Measuring T3 and T4 levels is an accurate means of diagnosing certain thyroid disorders. For example, Graves’ disease typically presents with increased T3 levels compared to T4. Certain severe illnesses or the use of steroid medication can result in a lower proportion of T3 to T4 [4].

Normal Thyroid Levels

Normal thyroid levels can vary slightly based on the lab’s range that conducts the thyroid testing, and most tests look at a combination of thyroid hormone and TSH levels. Thyroid testing can also measure free hormones in the blood or hormones already bound to sites. Total thyroid hormone levels measure both.

  • Normal values of TSH in adults range from 0.5 to 5.0 mIU/L.
  • Normal FT4 (free T4) levels among adults range from 0.7 to 1.9 ng/dL.
  • Total T4 levels in adults can range from 5.0 to 12.0 μg/dL.
  • Total T3 levels in adults can range from 80 to 220 μg/dL [3].

Using tests and comparing all of these levels together can help a healthcare provider determine if you have a thyroid problem.

Thyroid Disease Symptoms

Early signs of thyroid problems or ongoing symptoms of thyroid disease can vary based on the person and based on whether they have hypothyroidism or hyperthyroidism. There can be some slight overlap between the two, but an overactive thyroid can result in:

  • Unintended weight loss
  • Muscle weakness or tremors
  • Sudden anxiety, irritability, or nervousness
  • Sleep problems
  • Vision problems or eye irritation
  • Irregular menstrual periods, potentially even a cessation of the menstrual cycle [5]

An underactive thyroid can manifest as:

  • Increased fatigue
  • Sudden weight gain
  • Forgetfulness
  • Muscle weakness
  • Painful, stiff, swollen joints
  • Depression
  • Impaired memory
  • Frequent, heavy menstrual periods [6]

Diagnosing yourself based on symptoms alone can be highly inaccurate. The only way to know for sure if you have a thyroid disease is to get tested and receive an official diagnosis from a healthcare provider.

Understanding your thyroid hormone levels is a great way to better understand your overall health. If you’re unsure where to start, Everlywell offers an at-home thyroid test that measures for TSH, T3, T4, and thyroid peroxidase antibodies.

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References

1. Thyroid Disease. Cleveland Clinic. URL. Accessed January 7, 2022.

2. Thyroid gland. You and Your Hormones. URL. Accessed January 7, 2022.

3. What are Normal Thyroid Hormone Levels? UCLA Health. URL. Accessed January 7, 2022.

4. Thyroid Function Tests. American Thyroid Association. URL. Accessed January 7, 2022.

5. Hyperthyroidism (overactive thyroid). Mayo Clinic. URL. Accessed January 7, 2022.

6. Hypothyroidism (underactive thyroid). Mayo Clinic. URL. Accessed January 7, 2022.

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