What type of results do you get for a T3 (triiodothyronine) test?
Blood test reports, including T3 test reports, usually provide the following information:
- The name of the blood test or what was measured in your blood.
- The number or measurement of your blood test result.
- The normal measurement range for that test.
- Information that indicates if your result is normal or abnormal or high or low.
What are normal T3 levels?
Normal value ranges for any lab test, including T3 (triiodothyronine) tests, may vary slightly among different laboratories. Be sure to check your lab report’s reference range on your results. If you have any questions about your results, ask your healthcare provider.
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/or 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.
Should I be concerned if I have a low or high T3 (triiodothyronine) test result?
Total T3 test results are usually accurate. However, certain factors may interfere with the results, including certain medications or supplements and pregnancy. Your healthcare provider will consider these factors when interpreting your results.
A note from Cleveland Clinic
Seeing an abnormal test result can be stressful. Know that thyroid conditions are somewhat common and treatable. Your healthcare provider will let you know if you need to undergo further tests to determine the cause of the abnormal T3 level. Don’t be afraid to ask your provider questions. They’re there to help you.
