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Thyroid

Here’s a list of common thyroid blood tests with their purpose and the parameters measured:

1. TSH (Thyroid Stimulating Hormone)

  • Purpose:
    • This is the most common test for thyroid function. It measures the level of thyroid-stimulating hormone (TSH) in the blood to evaluate how well the thyroid gland is functioning. It helps detect hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid).
  • Parameters:
    • Normal range: 0.4–4.0 mIU/L (varies slightly based on lab and individual age)

2. Free T4 (Thyroxine)

  • Purpose:
    • Free T4 is the unbound form of thyroxine, a hormone produced by the thyroid. It is measured to check for thyroid function. High T4 levels indicate hyperthyroidism, while low levels suggest hypothyroidism.
  • Parameters:
    • Normal range: 0.8–1.8 ng/dL

3. Free T3 (Triiodothyronine)

  • Purpose:
    • Free T3 is the active thyroid hormone that affects metabolic rate and growth. This test is useful when hyperthyroidism is suspected, as T3 levels rise before T4 in hyperthyroid conditions.
  • Parameters:
    • Normal range: 2.3–4.2 pg/mL

4. Total T4

  • Purpose:
    • Measures both the free and bound thyroxine in the blood. This test is used to check for thyroid disease but is less precise than Free T4.
  • Parameters:
    • Normal range: 5.0–12.0 µg/dL

5. Total T3

  • Purpose:
    • Measures both the free and bound forms of triiodothyronine. It helps in diagnosing hyperthyroidism and monitoring thyroid therapy.
  • Parameters:
    • Normal range: 100–200 ng/dL

6. Thyroid Antibodies (TPOAb & TgAb)

  • Purpose:
    • TPOAb (Thyroid Peroxidase Antibody) and TgAb (Thyroglobulin Antibody) are used to diagnose autoimmune thyroid disorders like Hashimoto’s disease and Graves’ disease. Elevated antibodies indicate the immune system is attacking the thyroid.
  • Parameters:
    • TPOAb: <9 IU/mL (varies by lab)
    • TgAb: <20 IU/mL (varies by lab)

7. Thyroglobulin (Tg)

  • Purpose:
    • Used as a tumor marker in patients treated for thyroid cancer. It helps monitor for recurrence after thyroidectomy or radioactive iodine treatment.
  • Parameters:
    • Normal range: 3–40 ng/mL

8. Reverse T3 (rT3)

  • Purpose:
    • Measures the inactive form of T3. It is not commonly tested but may be used to evaluate thyroid function in critical illness or chronic stress when standard tests seem inconclusive.
  • Parameters:
    • Normal range: 10–24 ng/dL

Each of these tests provides insight into thyroid function and helps in diagnosing thyroid-related conditions like hypothyroidism, hyperthyroidism, thyroiditis, or thyroid cancer.