What is Free T3 (FT3)?
T3 (triiodothyronine) is a thyroid hormone produced directly by the thyroid when the body converts T4 (thyroxin) T3 (thyroxin). T3 and T4 regulate your body temperature, metabolism, and heart rate. Most of your T3 is attached to proteins. This test is for free T3, which is the T3 that is unbound to proteins. T3, both total and free, is measured to detect a problem with your thyroid hormones.
Why test free T3 (FT3)?
Measuring FT3 is significant because it represents triiodothyronine activity in the body. Testing T3 levels can help to discover risk factors for lifestyle diseases early, as free T3 is a crucial component of any thyroid profile. Symptoms of thyroid issues, such as depression, weakness, fatigue, sleeping problems, sensitivity to heat or cold, dry skin, hair loss, increased heart rate, and infertility, can be identified through T3 testing. Additionally, monitoring T3 levels allows you to track an existing thyroid condition as you make dietary and lifestyle changes or take medication
What do the results mean?
The results of different thyroid tests are interpreted together alongside your medical history.
Normal Free T3
A free T3 result within the reference range suggests that you are producing enough T4 and converting it adequately to T3. Normal values do not rule out thyroid problems. If you still have symptoms and your TSH, free T4, and free T3 are normal, we recommend testing your thyroid antibodies.
Low Free T3
A doctor interprets your free T3 results in the context of symptoms and other test results. Low free T3 could signify hypothyroidism or a reduced T4 to T3 conversion. In hypothyroidism, TSH is usually high, and T3 and T4 are normal to low.
Causes of low thyroid hormones include autoimmune thyroid disease (most often Hashimoto’s Thyroiditis), chronic inflammation, oxidative stress caused by lifestyle and diet, calorie restriction, low estrogen, low testosterone, and nutrient deficiencies (iodine, selenium, zinc, iron, chromium, copper, vitamin A, and B vitamins).
There is some evidence that eating a very low-carb or ketogenic diet may affect and lower thyroid function. The conversion of T4 to the active form of T3 is insulin-dependent. If you suddenly develop hypothyroid symptoms on a low carbohydrate diet, you may need to increase your carbohydrate intake. We recommend unrefined carbohydrates like whole grains (preferably gluten-free), beans, lentils, root vegetables, pumpkin, squash, fruit, and berries.
Common symptoms of hypothyroidism (underactive thyroid) include fatigue, feeling cold, often cold hands, feet, the nose tip, constipation, dry skin, weight gain or difficulty losing weight, puffy face, hoarseness, muscle weakness, stiff and achy muscles, slowed heart rate, dry and thinning hair, poor memory, and depression.
Symptoms of low T3
Low T3 levels, a condition known as hypothyroidism, can cause various symptoms due to the thyroid hormone's role in regulating metabolism. Common symptoms include fatigue, weakness, and weight gain. Individuals may also experience depression, dry skin, hair loss, and sensitivity to cold. Other signs include constipation, slow heart rate, and difficulty concentrating. If you notice these symptoms, it's important to seek medical evaluation to diagnose and manage the underlying cause effectively.
What causes high FT3 levels?
The levels of free T3 in your bloodstream are higher than expected. A doctor considers free T3 results in the context of symptoms, other test results, and your symptoms. In hyperthyroidism, TSH levels are usually on the low side or within range, and T3 and T4 are in range or high. High free T3 strongly suggests an overproduction of thyroid hormone (hyperthyroidism).
Graves’ disease (an autoimmune disorder that causes hyperthyroidism) can cause high free T3. Other causes include thyroid disease, pregnancy, iodine intake, exposure to toxic metals, certain medications, and consuming gluten. It may also be associated with iodine deficiency.
Note that reference ranges may be different during pregnancy.
Symptoms of high free T3
High T3 levels, known as hyperthyroidism, can cause a range of symptoms due to the thyroid hormone's role in speeding up metabolism. Common symptoms include rapid or irregular heartbeat, weight loss, and increased appetite. Individuals may also experience nervousness, anxiety, tremors, and sweating. Other signs include difficulty sleeping, heat intolerance, and frequent bowel movements. If you notice these symptoms, it’s important to seek medical evaluation to diagnose and treat the underlying cause effectively.
Preparations for this test
There is no preparation for this test.
On the day of the test
Remember to take I.D. with you when going to take a test. Do not take your thyroid medication until after you take this test.