Triiodothyronine (T3) Tests

The Triiodothyronine (T3) test is a blood test used to measure the level of T3, a hormone produced by the thyroid gland, in the bloodstream.

What is T3?

T3, or triiodothyronine, is a thyroid hormone that plays a crucial role in various bodily functions, including:

• Regulating metabolism
• Controlling growth and development
• Maintaining heart rate and rhythm
• Supporting nervous system function

Why is the T3 test performed?

The T3 test is typically performed to:

• Evaluate thyroid function, particularly in cases of suspected hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid)
• Monitor the effectiveness of treatment for thyroid disorders
• Diagnose and monitor thyroid-related conditions, such as Graves' disease or thyroiditis

How is the T3 test performed?

The T3 test involves a simple blood draw, usually from a vein in the arm. The blood sample is then sent to a laboratory for analysis.

Types of T3 tests

There are two main types of T3 tests:

• Total T3 (TT3): measures the total amount of T3 in the bloodstream, including both bound and free T3
• Free T3 (FT3): measures only the free, unbound T3 in the bloodstream, which is the biologically active form of the hormone

Interpretation of results

The interpretation of T3 test results depends on various factors, including:

• Age and sex
• Pregnancy status
• Medications or supplements being taken
• Underlying medical conditions

Normal T3 levels typically range from 75-195 ng/dL for TT3 and 2.5-3.9 pg/mL for FT3. Abnormal results may indicate:

• Hypothyroidism: low T3 levels
• Hyperthyroidism: high T3 levels
• Thyroid hormone resistance: elevated T3 levels with normal or low thyroid-stimulating hormone (TSH) levels

Limitations and potential interferences

Certain factors can affect the accuracy of T3 test results, including:

• Certain medications, such as birth control pills or steroids
• Pregnancy or recent childbirth
• Severe illness or stress
• Recent radioactive iodine treatment

It is essential to discuss any concerns or questions with a healthcare provider, who can provide personalized guidance and interpretation of test results.

Frequently Asked Questions (FAQs)

What is a T3 test?
Measures triiodothyronine hormone levels in blood.

Why is a T3 test done?
To diagnose thyroid disorders.

What does T3 measure?
Free and bound triiodothyronine in the blood.

How is a T3 test performed?
Blood sample drawn from a vein.

What is free T3?
T3 not bound to proteins in the blood.

What are normal T3 levels?
Vary by lab, typically 2.3-4.2 pg/mL for free T3.

How long does it usually take to get results?
Usually 1-2 days.

Do I need to prepare for a T3 test?
Fasting may be required.

What can affect T3 test results?
Certain medications and thyroid disorders.

Is a T3 test painful?
Typically no more painful than a standard blood draw.