The thyroid gland is a butterfly-shaped gland located in the neck. It is responsible for producing hormones that regulate metabolism and other important bodily functions.

Thyroid function tests are blood tests that measure the level of hormones produced by the thyroid gland, which include Thyroxine (T4), Triiodothyronine (T3), and Thyroid Stimulating Hormone (TSH).

Why are thyroid function tests done?

Thyroid function tests are performed for a variety of reasons:.

To diagnose thyroid disorders such as hypothyroidism, hyperthyroidism, and Hashimoto’s thyroiditis
To monitor treatment for thyroid disorders
To screen for thyroid disorders in people with a family history of thyroid disease
To evaluate fertility problems in women
To assess the risk of osteoporosis or cardiovascular disease

Types of thyroid function tests

There are several different types of thyroid function tests:.

1. Thyroid-stimulating hormone (TSH) test:

TSH tests are the most common type of thyroid function test. TSH is produced by the pituitary gland, which is located at the base of the brain.

TSH stimulates the thyroid gland to produce thyroid hormones, so a high level of TSH in the blood is an indication that the thyroid gland is not producing enough hormones. Conversely, a low level of TSH may indicate that the thyroid gland is producing too much hormone.

2. Total thyroxine (T4) test:

T4 is one of the two main hormones produced by the thyroid gland. A high level of T4 in the blood may indicate hyperthyroidism, while a low level may indicate hypothyroidism.

3. Free thyroxine (FT4) test:

FT4 is the unbound or “free” form of T4. Free T4 levels are more accurate than total T4 levels in determining thyroid function.

4. Triiodothyronine (T3) test:

T3 is the other main hormone produced by the thyroid gland. It is produced in smaller amounts than T4 but is more potent. T3 levels are often measured in conjunction with T4 levels to help diagnose hyperthyroidism or hypothyroidism.

5. Thyroid antibody tests:

Antibodies are proteins produced by the immune system to attack foreign substances or invaders such as viruses or bacteria.

In the case of thyroid antibody tests, they help diagnose autoimmune thyroid diseases such as Hashimoto’s thyroiditis and Graves’ disease.

How is the test done?

Thyroid function tests involve drawing a small amount of blood from a vein in the arm. No special preparation is required prior to the test.

The healthcare provider may ask the patient to stop taking certain medications temporarily if they can interfere with the test results. The test can be performed at any time of day, but is usually done in the morning, when hormone levels in the blood are at their highest.

Interpretation of results:

The normal range for thyroid hormone levels in adults varies from laboratory to laboratory, but generally includes:.

TSH: 0.4 to 4.0 milli-international units per liter (mIU/L)
T4: 5.0 to 12.0 micrograms per deciliter (mcg/dL)
FT4: 0.8 to 1.8 nanograms per deciliter (ng/dL)
T3: 80 to 200 nanograms per deciliter (ng/dL)

Abnormal results indicating an overactive or underactive thyroid gland may be due to:.

Hypothyroidism
Hyperthyroidism
Thyroiditis
Thyroid cancer

Further testing, such as an ultrasound, biopsy, or scan, may be necessary to confirm a diagnosis.

Conclusion:

Thyroid function tests are important in the diagnosis and management of thyroid disorders. They help assess the level of hormones produced by the thyroid gland, including TSH, T4, FT4 and T3.

These tests are simple and convenient, and can be performed at any time of the day. If you are experiencing symptoms of a thyroid disorder, or have a family history of thyroid disease, talk to your healthcare provider about having a thyroid function test.