Free T3

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)?

Unless this is ordered as a retest or for a specific reason, we recommend ordering this as part of a health test. Measuring FT3 is significant because it is an indicator of triiodothyronine activity in the body.

Health check
Discover your risk factors for lifestyle diseases in time to do something about them. Free T3 is an essential part of any thyroid profile.

Thyroid symptoms
Thyroid symptoms include depression, weakness, fatigue, sleeping problems, sensitivity to heat/cold, dry skin, hair loss, increased heart rate, and infertility.

Monitor an existing thyroid condition as you make dietary and lifestyle changes or take medication. We can send any results to your doctor

What do the results mean?

The results of different thyroid tests are interpreted together alongside your medical history.

Normal FT3

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.

What causes low FT3 levels?

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 when sticking to a very 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, and the tip of the nose, 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.

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.

There is no preparation for this test.

On the day
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.

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