Free T3 Test (FT3)

What is Free T3?

T3 (triiodothyronine) is one of the main hormones produced by the thyroid. Along with T4, T3 is responsible for regulating metabolism, heart rate, body temperature, mood, mental alertness and more.

T3 and T4 can either bind to proteins, or they can float freely in the blood. When T3 floats freely, it is considered free T3.

Are Free T3 and Total T3 the same?

No, free T3 and total T3 are different measurements. Free T3 is a measurement of the amount of unbound T3, floating freely in the blood. Total T3 is a measurement of the total amount of T3 in the body - bound and free. Free T3 is known as the active form of T3 and is viewed to be more active than its bound counterparts.

What is the Free T3 Normal Range?

The normal range for free T3 varies based on age. Below are the average reference ranges for age:

0 - 6 years: 2.4 - 4.2 pg/mL
7 - 17 years: 2.9 - 5.1 pg/mL
18 + years: 2.3 - 4. 2 pg/mL

Though these are the average ranges, individual measurements may be affected by certain disorders and conditions, such as pregnancy.

What Happens when Free T3 is Low?

When the body doesn’t produce enough T3 and T4 hormones, it can cause hypothyroidism.

Some of the symptoms of hypothyroidism include:

• Depression
• Irritability
• Weight gain
• Foggy brain
• Weak muscles

What Happens when Free T3 Levels are High?

If free T3 is too high, it may indicate an overactive thyroid. An overactive thyroid is referred to as hyperthyroidism.

Some of the symptoms of hyperthyroidism include:

• Increased heart rate
• Tremors
• Weight loss
• Sweating
• Anxiety

Why Should I test my Free T3?

You should test your free T3 in order to get a more thorough understanding of your thyroid’s functioning and/or monitor an ongoing thyroid issue. Keep in mind that measurements from free T3 alone cannot detect a thyroid issue. In addition to the free T3 test, we suggest testing your total T3, reverse T3, and T4 (free and total). If you’re interested in getting an overview of your thyroid health, we suggest looking into the thyroid with TSH panel.