What is Triiodothyronine Test

Triiodothyronine test is used to evaluate thyroid function. The thyroid is a gland in the lower front of your neck. It makes hormones that affect many body parts and systems, including the system that affects how quickly your body burns fuel for energy (metabolism). You may have this test:

• To monitor treatment for a thyroid disorder.
• To help diagnose various thyroid conditions, including:
  • An overactive thyroid (hyperthyroidism).
  • An underactive thyroid (hypothyroidism).
  • Inflammation of the thyroid (thyroiditis).

What is being tested?

This test measures the level of triiodothyronine (T3) in the blood. T3 is one of the two main hormones made by the thyroid gland. This test is often done with thyroid tests that test other thyroid hormones.

What kind of sample is taken?

A blood sample is required for this test. It is usually collected by inserting a needle into a blood vessel.

How do I prepare for this test?

Follow instructions from your health care provider about changing or stopping your regular medicines. Many medicines can affect thyroid hormones, including birth control pills, estrogen, and aspirin.

Tell a health care provider about:

• Any allergies you have.
• All medicines you are taking, including vitamins, herbs, eye drops, creams, and over-the-counter medicines.
• Any blood disorders you have.
• Any surgeries you have had.
• Any medical conditions you have.
• Whether you are pregnant or may be pregnant.

How are the results reported?

Your test results will be reported as a value that indicates how much T3 is in your blood. This will be given as nanograms of T3 per deciliter of blood (ng/dL).

Your health care provider will compare your results to normal ranges that were established after testing a large group of people (reference ranges). Reference ranges may vary among labs and hospitals. For this test, common reference ranges are:

• 1–3 days old: 100–740 ng/dL.
• 1–11 months old: 105–245 ng/dL.
• 1–5 years old: 105–270 ng/dL.
• 6–10 years old: 95–240 ng/dL.
• 11–15 years old: 80–215 ng/dL.
• 16–20 years old: 80–210 ng/dL.
• 20–50 years old: 70–205 ng/dL.
• Older than 50 years: 40–180 ng/dL.

What do the results mean?

A result that is within your reference range is considered normal. This means that you have a normal amount of T3 in your blood.

A result that is higher than your reference range means that you have more T3 in your blood than normal. This may mean that:

• You have hyperthyroidism.
• You have thyroiditis.
• You are taking more thyroid medicine than you need.
• You are pregnant.
• You have hepatitis.

A result that is lower than your reference range means that you have less T3 in your blood than normal. This may mean that you have:

• Hypothyroidism.
• Problems with your pituitary gland function.
• Problems with your hypothalamus gland function.
• A lack of certain nutrients in your diet (malnutrition).
• Liver disease.
• Kidney disease.

Talk with your health care provider about what your results mean.

Questions to ask your health care provider

Ask your health care provider, or the department that is doing the test:

• When will my results be ready?
• How will I get my results?
• What are my treatment options?
• What other tests do I need?
• What are my next steps?

Summary

• The triiodothyronine test is used to evaluate thyroid function. It measures the level of triiodothyronine (T3) in your blood. T3 is one of the two main hormones made by the thyroid gland.
• This test is often done with thyroid tests that test other thyroid hormones.
• Talk with your health care provider about what your test results mean.