Posted September 30, 2022 by Anusha ‐ 4 min read
A T3 test or triiodothyronine test is a blood test that helps diagnose thyroid conditions, specifically hyperthyroidism.
Other names of T3 test
Other names for a T3 test include:
Thyroid function test.
What is a T3 test?
A T3 (triiodothyronine) test helps diagnose thyroid conditions, particularly hyperthyroidism (overactive thyroid).
Your thyroid is a small, butterfly-shaped gland located at the front of your neck under your skin.
It’s a part of your endocrine system.
Triiodothyronine, also known as T3, is one of the two main thyroid hormones.
Thyroxine, or T4, is the other hormone.
Procedure of T3 test
You can expect to experience the following during a blood test, or blood draw:
You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
Once they’ve located a vein, they’ll clean and disinfect the area.
They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
After they insert the needle, a small amount of blood will collect in a test tube.
Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
They’ll place a bandage over the site, and you’ll be finished.
The entire procedure usually takes less than five minutes.
Normal T3 levels
Normal T3 level ranges vary based on age. In general, normal ranges for T3 for healthy people include:
Children 1 to 5 years old: 106 – 203 nanograms per deciliter (ng/dL).
Children 6 to 10 years old: 104 – 183 ng/dL.
Children 11 to 14 years old: 68 – 186 ng/dL.
Adolescents 15 to 17 years old: 71 – 175 ng/dL.
Adults 18 to 99 years old: 79 – 165 ng/dL.
Normal free T3 levels
Providers don’t usually order free T3 tests because they’re not as reliable, but it is possible to test these levels. In general, normal ranges of free T3 for healthy people include:
Infants up to 3 days old: 1.4 – 5.4 picograms per milliliter (pg/mL).
Infants 4 to 30 days old: 2.0 – 5.2 pg/mL.
Babies 1 month to 1 year old: 1.5 – 6.4 pg/mL.
Children 1 to 6 years old: 2.0 – 6.0 pg/mL.
Children 7 to 11 years old: 2.7 – 5.2 pg/mL.
Children 12 to 17 years old: 2.3 – 5.0 pg/mL.
Adults 18 to 99 years old: 2.3 – 4.1 pg/mL.
What happens when T3 levels are high?
Higher-than-normal T3 levels typically indicate hyperthyroidism (overactive thyroid).
Hyperthyroidism has several causes, including Graves’ disease (an autoimmune condition), thyroid nodules and thyroiditis (inflammation of your thyroid gland).
Hyperthyroidism speeds up your metabolism, which can be dangerous to your health. Some symptoms of hyperthyroidism include:
Unexplained weight loss.
Feeling shaky and nervous.
Increased bowel movements.
Rapid or irregular heartbeat (arrhythmia).
If you’re experiencing symptoms of hyperthyroidism, it’s important to contact your healthcare provider.
If you’ve already been diagnosed with hyperthyroidism, T3 tests can help determine how severe it is. In general, the more elevated your T3 levels, the more severe the hyperthyroidism is.
What happens when T3 levels are low?
Lower-than-normal T3 levels may indicate you have hypothyroidism (underactive thyroid).
However, healthcare providers don’t typically rely on T3 tests to diagnose hypothyroidism because it’s usually the last of the thyroid function tests to come back abnormal.
In addition, some people can have severe hypothyroidism with a high TSH level and a low free T4 level but have a normal T3 level.
Lower-than-normal T3 levels can also be due to medications like steroids and amiodarone (arrhythmia medication) and severe illness.
These factors can decrease the amount of T4 (inactive hormone) your body converts into T3 (active hormone), resulting in a lower level of T3.
Risks of T3 test
Blood tests are a very common and essential part of medical testing and screening.
There’s very little risk to having a T3 blood test.
You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.