The T3 test measures triiodothyronine in blood to help doctors diagnose hyperthyroidism. The total triiodothyronine (T3) test is one of several tests used to diagnose thyroid disorders. T3 is an active thyroid hormone that your body creates by converting thyroxine (T4) into triiodothyronine. The 3 and 4 in the names represent the number of iodine atoms it has.
T3 helps maintain muscle control, brain function and development, heart and digestive functions. High or low T3 levels may indicate an overactive or underactive thyroid.
What is the Thyroid?
The thyroid gland is located in front of your neck. It has right and left lobes that resemble a butterfly. This gland produces hormones that help control your metabolism, which is how your body uses energy. Disorders that affect thyroid function can either speed up or slow down metabolic processes.
Thyroid problems can cause a wide range of symptoms and affect your:
→ Appetite and weight
→ Body temperature
→ Energy level
→ Heart rate (Hyperthyroidism causes a fast heartbeat)
Hyperthyroidism Symptoms:
If you have symptoms that might point to thyroid problems, this test helps your doctor identify the cause.
What Is T3?
T3 (triiodothyronine) is a hormone that helps control many body functions, including growth, body temperature, and heart rate. When your thyroid gland is working properly, it makes and releases a hormone called thyroxine, or T4. Your blood carries T4 around your body where your liver, brain, and other tissues turn some of it into triiodothyronine, or T3.
There are two types of T3 in your blood:
→ Bound T3, which attaches to proteins that help carry the hormone through the body.
→ Free T3, which is not attached to proteins.
The Total T3 test measures levels of both the bound and free types of T3.
More about the T3 test:
The T3 test can also help your doctor identify thyroid cancer and other uncommon conditions that can affect your thyroid.
T3 tests are often useful to diagnose hyperthyroidism or to determine the severity of the hyperthyroidism. Patients who are hyperthyroid will have an elevated T3 level. In some individuals with a low TSH, only the T3 is elevated and the FT4 or FTI is normal.
T3 testing rarely is helpful in the hypothyroid patient, since it is the last test to become abnormal. Patients can be severely hypothyroid with a high TSH and low FT4 or FTI, but have a normal T3.
Doctors order T3 total tests when they’re checking a person’s thyroid function. Doctors may order the T3 test when a child's symptoms or previous blood tests suggest a thyroid problem. The T3 test is particularly useful in diagnosing hyperthyroidism. In this condition, the thyroid overproduces hormones, causing symptoms such as a fast heart rate, weight loss, trembling, and sweating.
The T3 test simply measures how much of this hormone is present in your blood. If the level is either abnormally high or abnormally low, it can be an indicator of thyroid disease. However, this test is generally more useful for diagnosing hyperthyroidism (overactive thyroid) than hypothyroidism (underactive thyroid), and it's typically combined with measures of other thyroid hormone levels rather than taken alone.
Total T3 tests are generally ordered when you have symptoms that are consistent with thyroid disease, especially if you have an elevated risk. Risk factors include being female, being under the age of 40, and having family members who are diagnosed with thyroid disorders.
Your healthcare provider will likely order other measurements of thyroid function at the same time as T3 test including tests of thyroid stimulating hormone (TSH) and T4. Tests to look for antibodies that indicate autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease.
The T3 test, as well as other thyroid tests, are performed on blood samples. The process for drawing blood for these tests is generally quick, simple, and low-risk.
What do normal, high, and low levels mean?
Normal T3 levels in the blood range from 71 - 180 ng/dL (nanograms per deciliter).
If your levels are higher than normal, that could mean you have an overactive thyroid (hyperthyroidism) or an uncommon condition such as thyroid cancer.
If your levels are lower than normal, that could be a sign of an underactive thyroid (hypothyroidism) or chronic illness. Your doctor will need to order other tests in order to diagnose these issues.
Why is the Free T3 blood test better than the Total T3 blood test?
Measuring total T3 (both bound and unbound) may give misleading information if the binding proteins are increased or decreased
Therefore, most healthcare providers today rely on the free T3 blood test instead of the total T3 blood test.
In more than 70% of cases, hyperthyroidism is due to Graves’ disease, which occurs most often in females and can run in families. Nodules and lumps that grow on the thyroid can also cause hyperthyroidism. Doctors refer to this as toxic nodular goiter.
How to interpret Thyroid test results?
The table below provides examples of test results and their possible interpretation:
| TSH | FREE T4 | FREE OR TOTAL T3 | THYROID FUNCTION |
|---|---|---|---|
| Normal | Normal | Normal | Normal thyroid function |
| High | Normal | Normal | Subclinical hypothyroidism |
| High | Low | Normal or low | Primary hypothyroidism related to the thyroid gland |
| Low or undetectable | Normal | Normal | Subclinical hyperthyroidism |
| Low | High | High | Primary hyperthyroidism related to the thyroid gland |
| Low | Low | Low or normal | Secondary hypothyroidism related to the pituitary gland |
| Normal or high | High | High | Secondary hyperthyroidism related to pituitary gland |
Subclinical hypothyroidism and hyperthyroidism are conditions defined by abnormal TSH test results with normal T3 and T4 levels. These subclinical conditions often cause no symptoms or only very mild ones. Some subclinical thyroid conditions may progress to outright hypothyroidism or hyperthyroidism over time.
References:
American Thyroid Association, Thyroid Function Tests; https://www.thyroid.org/thyroid-function-tests
Lab Tests Online, American Association for Clinical Chemistry; T3 (Free and Total); https://labtestsonline.org/tests/t3-free-and-total
National Institute of Diabetes and Digestive and Kidney Diseases, Thyroid Tests; https://www.niddk.nih.gov/health-information/diagnostic-tests/thyroid
A.D.A.M. Medical Encyclopedia. Free T4 Test - https://medlineplus.gov/ency/article/003517.htm
A.D.A.M. Medical Encyclopedia. Hyperthyroidism - https://medlineplus.gov/ency/article/000356.htm
A.D.A.M. Medical Encyclopedia. T3 Test - https://medlineplus.gov/ency/article/003687.htm
A.D.A.M. Medical Encyclopedia. TSH Test - https://medlineplus.gov/ency/article/003684.htm
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An abnormally high level of T3 isn't generally a sign of thyroid disease by itself, but it is considered along with TSH and T4 levels.
A high T3 level may indicate:
→ Hyperthyroidism if accompanied by a low TSH level
→ Graves' disease if accompanied by a low TSH level and positive tests to detect certain antibodies
→ Toxic nodular goiter (an enlarged thyroid gland that contains a small rounded mass or masses called nodules, which produce too much thyroid hormone.)
→ Liver disease
→ A rare condition called T3 thyrotoxicosis [a clinical state of inappropriately high levels of circulating thyroid hormones (T3 and/or T4) in the body from any cause. It is often incorrectly used interchangeably with hyperthyroidism, which is a form of thyrotoxicosis caused by excessive endogenous thyroid hormone production.]
→ High T3 can also be due to pregnancy or the use of medications containing estrogen.
An abnormally low T3 level may indicate:
→ Hypothyroidism, if accompanied by a high TSH level
→ Hashimoto's thyroiditis, if accompanied by a high TSH level and positive tests to detect certain antibodies
→ Malnutrition/starvation
→ A severe short-term illness or some long-term illnesses
Keep in mind that this test has some limitations, which are that:
→ T3 is largely bound to blood proteins (99.7%)
→ Only unbound T3 is active
How to interpret Total T3 together with TSH?
What is TSH?
Thyroid-Stimulating Hormone (TSH) is a hormone produced by the pituitary gland in the brain. Its primary role is to regulate the thyroid gland's activity by stimulating the production and release of thyroid hormones (T3 and T4). TSH levels in the bloodstream rise when thyroid hormone levels are too low, signaling the thyroid gland to increase hormone production. Conversely, when thyroid hormone levels are too high, TSH levels decrease to reduce thyroid hormone production. TSH is a crucial marker used in assessing thyroid function, with abnormal levels indicating potential thyroid disorders, such as hyperthyroidism or hypothyroidism.
How to interpret those markers together:
Interpreting Total T3 (triiodothyronine) levels together with Thyroid-Stimulating Hormone (TSH) levels can provide valuable insights into a person's thyroid function. TSH is often considered the most sensitive marker for thyroid function, while Total T3 provides information about the actual thyroid hormone levels in the bloodstream. Here's how to interpret these two tests together:
Normal Thyroid Function:
Hyperthyroidism (Overactive Thyroid):
Hypothyroidism (Underactive Thyroid):
Secondary or Tertiary Hypothyroidism:
It's important to note that Total T3 measures the total amount of T3 in the bloodstream, including both free (biologically active) and bound T3. While it can provide valuable information, some healthcare providers prefer to use Free T3 levels for a more accurate assessment of thyroid function, as discussed in a previous section above.
How to treat elevated Total T3 levels?
Elevated Total T3 (triiodothyronine) levels can be a sign of hyperthyroidism, a condition where the thyroid gland produces an excess of thyroid hormones, including T3. Treatment for elevated Total T3 levels typically involves addressing the underlying cause, which is often an overactive thyroid. Here are common treatment approaches:
Anti-Thyroid Medications:
In cases of hyperthyroidism, healthcare providers may prescribe anti-thyroid medications such as methimazole or propylthiouracil (PTU). These drugs help reduce the production of thyroid hormones by the thyroid gland.
Radioactive Iodine (RAI) Therapy:
Radioactive iodine therapy involves the administration of a radioactive substance that selectively destroys thyroid cells, reducing hormone production. This treatment is often used when antithyroid medications are ineffective or not well-tolerated.
Beta-Blockers:
Beta-blockers like propranolol may be prescribed to manage symptoms of hyperthyroidism, such as rapid heart rate, tremors, and anxiety. Beta-blockers do not treat the underlying thyroid condition but can provide relief from certain symptoms.
Surgery (Thyroidectomy):
In some cases, surgical removal of part or all of the thyroid gland (thyroidectomy) may be recommended, especially when medications and radioactive iodine therapy are not suitable or effective.
Monitoring:
Regular monitoring of thyroid function through blood tests, including Total T3 and other thyroid markers, is crucial to assess the effectiveness of treatment and adjust medication doses as needed.
The specific treatment approach depends on the underlying cause of the elevated Total T3 levels, the severity of hyperthyroidism, and individual patient factors. It's essential to work closely with a healthcare provider or an endocrinologist to determine the most appropriate treatment plan for your specific situation.
Additionally, lifestyle modifications, such as adopting a healthy diet, managing stress, and getting enough rest, can complement medical treatment and help support thyroid health. It's essential to follow your healthcare provider's recommendations and attend regular follow-up appointments to ensure that your thyroid function returns to a healthy balance.
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Low Total T3 (triiodothyronine) levels typically indicate a deficiency in thyroid hormone production or conversion, a condition known as hypothyroidism.
This can result from various underlying causes, including:
- Hashimoto's thyroiditis,
- iodine deficiency,
- certain medications,
- or pituitary gland dysfunction.
Hypothyroidism can lead to a range of symptoms, including:
- fatigue,
- weight gain,
- cold intolerance,
- dry skin,
- and cognitive impairment.
Treatment for low Total T3 levels involves hormone replacement therapy with synthetic thyroid hormones, primarily levothyroxine (T4).
The goal is to restore thyroid hormone levels to the normal range, as T4 can be converted into the active T3 in the body as needed. The dosage of levothyroxine is adjusted based on regular blood tests, including TSH, Free T4, and Free T3, to ensure thyroid hormone levels are optimized and symptoms are relieved. It's crucial to work closely with a healthcare provider to determine the appropriate dosage and monitor thyroid function regularly to achieve and maintain a healthy thyroid balance.
Some lifestyle and dietary practices may complement medical treatment and support thyroid health:
Eat a Balanced Diet: Consume a diet rich in nutrients, including iodine and selenium, which are essential for thyroid function. Good sources of iodine include seafood, dairy products, and iodized salt. Selenium-rich foods include Brazil nuts, fish, and whole grains.
Manage Stress: Chronic stress can impact thyroid function. Practice stress management techniques such as meditation, yoga, deep breathing exercises, or relaxation techniques to reduce stress levels.
Exercise Regularly: Engaging in regular physical activity can help support overall health and metabolism, which can indirectly benefit thyroid function.
Get Adequate Sleep: Prioritize good sleep hygiene and aim for 7-9 hours of quality sleep per night to support overall well-being, including thyroid health.
Avoid Goitrogenic Foods: Some foods contain compounds known as goitrogens that can interfere with thyroid function. These include raw cruciferous vegetables (e.g., broccoli, cabbage, cauliflower), soy products, and millet. Cooking these foods can help reduce their goitrogenic effects.
Limit Processed Foods: Minimize your intake of processed and sugary foods, as they can contribute to inflammation and hormonal imbalances that may affect thyroid function.
Stay Hydrated: Proper hydration is essential for overall health and can help support metabolic processes.
Important note:
While these lifestyle and dietary practices can promote overall well-being and may have a positive impact on thyroid health, it's crucial to consult with a healthcare provider if you have concerns about your thyroid function or low Total T3 levels. Natural methods alone may not be sufficient to address thyroid disorders, and medical evaluation and treatment are often necessary to restore thyroid hormone balance. Always follow your healthcare provider's guidance and treatment recommendations for thyroid-related conditions.
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