Thyroid Function Test (TFT)

If you have been experiencing fatigue, weight changes, or mood swings, your doctor might suggest you take a Thyroid Function Test (TFT). A TFT is a blood test that measures the levels of thyroid hormones and thyroid-stimulating hormones (TSH) in your bloodstream. This test helps your doctor evaluate the functioning of your thyroid gland, which regulates many of your body’s essential functions.

What is the thyroid gland?

The thyroid gland is a butterfly-shaped gland located in the neck. It produces and releases hormones that regulate your metabolism and energy levels. The thyroid hormones include thyroxine (T4) and triiodothyronine (T3), which help regulate the body’s metabolism, heart rate, and temperature. The thyroid gland also produces calcitonin, a hormone that regulates calcium levels in the body.

Why is a TFT performed?

A TFT is usually performed when your doctor suspects that you have a thyroid disorder, such as hypothyroidism or hyperthyroidism. Hypothyroidism occurs when the thyroid gland doesn’t produce enough hormones, while hyperthyroidism occurs when the gland produces too much. Both conditions can cause a range of symptoms, including fatigue, weight changes, and mood swings.

How is a TFT performed?

A TFT is a simple blood test that can be performed at your doctor’s office or a laboratory. Before the test, your doctor might ask you to stop taking certain medications that can affect your thyroid hormone levels. You will also need to fast for a few hours before the test. During the test, a healthcare provider will take a blood sample from your arm using a small needle. The sample will then be sent to a laboratory for analysis.

What do the results mean?

The results of a TFT can help your doctor diagnose a thyroid disorder and determine the appropriate treatment. The normal ranges for the thyroid hormones and TSH levels are as follows:

Thyroid Hormones Normal Range

Thyroid Hormones Normal Range
T4 5.0-12.0 ug/dL
T3 100-200 ng/dL
TSH 0.4-4.0 mIU/L

If the thyroid hormone levels are too high or too low, your doctor might recommend further testing or prescribe medication to balance your hormone levels. The results of a TFT should always be interpreted in conjunction with your symptoms and medical history.


Is a TFT painful?

No, a TFT is a simple blood test that is generally painless. You might feel a small pinch when the needle is inserted, but the discomfort should be minimal.

Can I eat before a TFT?

You will need to fast for a few hours before the test. Your doctor might recommend that you avoid food and drink, except for water, for up to 12 hours before the test.

How long does it take to get TFT results?

The results of a TFT usually take a few days to a week to become available.


American Thyroid Association. (n.d.). Thyroid Function Tests. Retrieved March 21, 2023, from

Mayo Clinic. (2021, March 31). Thyroid function tests.

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