Thyroid Profile (Free T4) medical test
Learn about Thyroid Profile (Free T4) medical tests, including what the tests are used for, why a doctor may order a test, how a test will feel, and what the results may mean.
What is Thyroid Profile (Free T4)?
A thyroxine test helps diagnose disorders of the thyroid. The thyroid is a small, butterfly-shaped gland located near the throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. Thyroxine, also known as T4, is a type of thyroid hormone. This test measures the level of T4 in your blood. Too much or too little T4 can indicate thyroid disease.The thyroid-stimulating hormone (TSH) test measures the amount of TSH in the blood. The results convey how well the thyroid is functioning. Doctors can use TSH test results to diagnose thyroid disorders, such as hypothyroidism and hyperthyroidism.
What the Thyroid Profile (Free T4) test used for?
Your doctor may order a T4 test if a thyroid-stimulating hormone (TSH) test has come back with abnormal results. A T4 test will help your doctor determine what type of problem is affecting your thyroid. You may need this test if your healthcare provider wants to find out whether you have a thyroid-related condition, such as hyperthyroidism, which means an overactive thyroid, or hypothyroidism, which means an underactive thyroid. If you do have a thyroid problem, you may have the test to monitor changes or treatment.
How is the procedure performed?
A number of drugs can interfere with your T4 levels, especially total T4, so it’s important to tell your doctor what medications you’re taking. You may need to temporarily stop taking certain drugs before the test to help ensure accurate results. It’s also important to let your doctor know if you may be pregnant. A blood sample drawn from a vein in your arm. You may want to wear a shirt with sleeves that can easily be rolled up to make it easier to collect the blood sample.
What will be the results interprets?
Results for children vary based on age. Talk to your doctor about the normal ranges expected for your child. There may also be some variation between labs. As with any test result, if it falls outside the expected range, talk to your doctor about what the results may mean in regards to your own personal health condition.
| Normal range (Adult) | |
|---|---|
| Total T4 test | 5.0 - 12.0 micrograms per deciliter (μg/dL) |
| Free T4 test | 0.8 - 1.8 nanograms per deciliter (ng/dL). |
An abnormal result on the T4 test alone may not give your doctor enough information to fully understand or diagnose your condition. They may also need to consider the results of T3 and TSH levels for a more complete picture.
According to guidelines issued by the American Association of Clinical Endocrinologists (AACE) and the American Thyroid Association (ATA), a TSH value:
| TSH range (milliunits/litre) | |
|---|---|
| Normal | 0.4 - 4.0 |
| Subclinical hypothyroidism | 4.7 - 10 |
| Overt (symptomatic) hypothyroidism | 0.1 - 0.5 |
| Subclinical hyperthyroidism | 4.7 - 10 |
| Overt hyperthyroidism | Less than 0.1 |
Pregnancy hormones naturally increase the levels of certain thyroid hormones in the blood. This is essential for the development of the fetal brain and nervous system. At the same time, the levels of TSH in the blood decrease. As a result, doctors use lower reference ranges for pregnant women. The lower TSH range is decreased by around 0.1 to 0.2 mU/l and the upper limit is decreased by around 0.5 to 1.0 mU/l.
Other related tests for Thyroid Function Tests: Thyroid Functional Test, Thyroid Stimulating Hormone (TSH)