Thyroid function tests are a group of blood tests that are used to evaluate how well the thyroid gland is functioning. The thyroid gland is a small, butterfly-shaped gland located in the front of the neck, and it plays a crucial role in regulating various metabolic processes in the body.

The most common thyroid function tests include:

1. Thyroid-stimulating hormone (TSH) test: TSH is produced by the pituitary gland and stimulates the thyroid gland to produce thyroid hormones. High levels of TSH may indicate an underactive thyroid (hypothyroidism), while low levels may indicate an overactive thyroid (hyperthyroidism).
2. Free thyroxine (FT4) test: FT4 is the main thyroid hormone produced by the thyroid gland. It helps regulate metabolism in the body. Abnormal levels of FT4 can indicate thyroid dysfunction.
3. Total or Free triiodothyronine (T3) test: T3 is another thyroid hormone that helps regulate metabolism. It is usually measured along with other thyroid function tests to provide a more comprehensive picture of thyroid function.
4. Thyroid peroxidase antibody (TPOAb) test: This test measures the presence of antibodies against the enzyme thyroid peroxidase. Elevated TPOAb levels are often seen in autoimmune thyroid diseases such as Hashimoto’s thyroiditis and Graves’ disease.
5. Thyroglobulin (Tg) test: Thyroglobulin is a protein produced by the thyroid gland. This test is primarily used in monitoring thyroid cancer, as elevated levels of thyroglobulin may indicate the presence of residual or recurrent cancer cells.

The normal reference range for thyroid function tests can vary slightly depending on the laboratory and the specific assay used.

1. Thyroid-stimulating hormone (TSH):
   • Normal range: 0.4 – 4.0 mIU/L
2. Free thyroxine (FT4):
   • Normal range: 0.8 – 1.8 ng/dL (or 10 – 23 pmol/L)
3. Total or Free triiodothyronine (T3):
   • Normal range: 80 – 200 ng/dL (or 1.2 – 3.1 nmol/L)

It is important to note that these reference ranges are approximate and can vary slightly depending on the laboratory and the specific method used for testing. Additionally, reference ranges may be adjusted for specific age groups (e.g., children, older adults), pregnancy, or other factors.

It’s essential to interpret the results of thyroid function tests in conjunction with a person’s clinical symptoms, medical history, and physical examination. Abnormal results outside the reference range should be discussed with a healthcare provider for further evaluation and appropriate management.

These tests, along with a patient’s symptoms and physical examination, help healthcare providers diagnose thyroid disorders such as hypothyroidism, hyperthyroidism, thyroid nodules, or thyroid cancer. It is important to note that interpretation of thyroid function tests should be done by a healthcare professional, as results can vary based on individual circumstances.