The thyroid gland impacts our overall health by regulating metabolism, the chemical processes that convert food to energy, and keep our cells working. The gland affects vital functions, such as heart rate, digestion, body temperature, and energy levels.
A T3 test measures levels of triiodothyronine, a thyroid hormone also known as T3, in the body. It’s one of several thyroid function tests that evaluates how well the thyroid gland is working.
This guide provides a basic overview of how the thyroid gland functions and the role of T3 hormones in the body. It also provides information about T3 testing, what it means if your T3 levels are too low or too high, and options for treatment.
The American Thyroid Association reports that up to 60% of people with thyroid disease don’t know they have the condition. Left undiagnosed, these disorders can increase the risk of heart disease, osteoporosis, and infertility. In pregnant women, it can lead to miscarriage, early delivery, or developmental problems in babies.
A T3 test, also known as a triiodothyronine test or thyroid function test, measures levels of T3 in the body to provide insight into how well the thyroid is working. Thyroid disorders occur when there’s too much or too little of any thyroid hormone in the body. In addition to T3, thyroid hormones include thyroxine (T4) and thyroid-stimulating hormone (TSH).
Your doctor may recommend T3 testing to evaluate thyroid function if:
A blood sample is used to test levels of triiodothyronine in your body.
Let your doctor know of any medicines or supplements that you’re taking, as these may affect your test results. It’s important that you do not stop taking any medication unless specifically requested by your doctor.
Otherwise, no preparation is required for a T3 blood test.
The thyroid is a butterfly-shaped gland with two lobes, located in the lower part of the neck just below the larynx.
This gland produces vital hormones that affect the body’s metabolism and how it creates energy for important body functions. Thyroid hormones affect:
The thyroid gland produces two types of thyroid hormones:
The thyroid produces only about 20% of the T3 in the body. The rest is T4 that’s converted to T3 in the liver, kidneys, and brain. This is accomplished by enzymes called deiodinases that remove one of the iodine atoms. While both T3 and T4 affect metabolism, T3 is considered the more active hormone.
Most of the T3 in the body travels through the bloodstream attached to proteins. This is called bound T3, and it doesn’t affect body tissues. Free T3 is unbound and can enter body tissues.
Levels of T3 and T4 are controlled by the pituitary gland, which detects how much T4 is in the body. If the pituitary gland senses that increased levels of hormones are needed, it activates the thyroid gland by releasing thyroid-stimulating hormones (TSH). Thyroid disorders result when T3, T4, or TSH levels are out of normal range.
When there’s too much T3 in the body, you can develop hyperthyroidism. Symptoms may include:
Causes of an overactive thyroid include:
When there’s too little T3 in the body, you can develop hypothyroidism, or a slowing of the body’s functions. Symptoms may include:
Hypothyroidism is most common in women and people over the age of 50. It’s typically caused by chronic illness or thyroiditis, including Hashimoto’s disease.
There are two types of tests for measuring levels of T3 in the bloodstream. Both are performed on blood samples.
If your physician recommends a T3 test, you’re given a doctor’s order that you can take to a clinic or laboratory to have the test performed.
A clinician takes the blood sample using a small needle syringe, usually from a vein on your arm.
You can purchase T3 tests directly on some websites without consulting a doctor. This includes a test requisition that you can take to a laboratory or a test kit to use at home.
Thyroid disorders have many causes. Your physician can recommend a treatment plan based on your diagnosis, age, and medical history.
Most thyroid disorders are lifelong conditions but can be managed with appropriate treatment.
If you have an overactive thyroid, your doctor may recommend treatment that involves:
When your body isn’t making enough thyroid hormones, your doctor may recommend thyroid hormone replacement therapy to make up for the one that you’re lacking.
A commonly used synthetic hormone is levothyroxine, which is available under a number of different brand names. Thyroid hormones come in pill form and are best taken at the same time each day to ensure consistent levels in the bloodstream. Your doctor may need to adjust dosages based on regular testing of your hormone levels to ensure proper thyroid function.
Levothyroxine is a T4 replacement but is also used to treat low levels of T3, as most of the T3 in the body is converted from T4. This conversion process functions normally in patients with hypothyroidism, so maintaining levels of T4 helps ensure adequate levels of T3.
If you’re taking thyroid hormones, your physician will monitor your improvement with regular blood tests to check your hormone levels and adjust dosages if necessary.
A synthetic form of T3 called liothyronine is available, but at this time, clinical studies don’t support its use for treating hypothyroidism. Liothyronine can cause fluctuations in T3 levels and numerous side effects.
Your doctor can recommend the appropriate treatment.
Yes. You can find T3 tests or thyroid panels that include screening for T3 available for purchase on some websites.
Results considered normal vary depending on the laboratory as well as factors, such as your age and health. It’s best to speak to your physician to interpret your results, but the following are considered typical normal T3 ranges for adults:
There are different ranges for pediatric patients under the age of 20.
There are many reasons T3 levels may be outside of the normal range, including pregnancy, liver disease, certain medications, and chronic illness. Your physician can discuss your results with you and recommend additional tests if there are concerns.
You may require blood tests to check the levels of other hormones in your body. Reviewing levels of T4 or TSH, along with T3, gives a more accurate picture of thyroid function. In some cases, ultrasound and other imaging tests may be required.
Women are more likely than men to develop thyroid disease, especially after pregnancy or menopause. About 12.5% of women develop a thyroid condition in their life. This may result in difficulties with menstruation, ovulation, and pregnancy. If thyroid disorders are untreated in pregnant women, they can cause low birth weight, miscarriage, or problems with the baby’s growth and development.
Yes. The thyroid is vital to growth and development and can have a significant impact on babies, children, and adolescents if left untreated. Some effects include delayed growth resulting in short stature, delayed development of permanent teeth, delayed puberty, and poor mental development.
To learn more about thyroid disorders and testing for these conditions, use the following resources.
|American Association of Clinical Endocrinologists||www.empoweryourhealth.org||Overview of how the thyroid works|
|U.S. National Library of Medicine||www.medlineplus.gov||General information about thyroid diseases|
|Texas Department of State Health Services||www.dshs.texas.gov||FAQs on hypothyroidism in infants|
|U.S. Office on Women’s Health||www.womenshealth.gov||Fact sheet about thyroid disease in women|
|Merck Manual||www.merckmanuals.com||Overview of thyroid gland disorders|