Free T3 and Free T4 Blood Test Panel

The Free T3 and Free T4 Blood Test Panel panel contains 2 tests with 2 biomarkers.

Brief Description: The Free T3 and Free T4 Blood Test Panel is used to assess the levels of the two main thyroid hormones circulating unbound in the bloodstream. The thyroid, a butterfly-shaped gland situated in the front of the neck, plays a pivotal role in metabolism, growth, and development by producing thyroid hormones. Among these, triiodothyronine (T3) and thyroxine (T4) are the most significant. While most of the T3 and T4 in the blood is bound to proteins, a tiny fraction remains free (unbound) and is biologically active. This panel specifically measures this active fraction, giving a more accurate representation of thyroid function.

Collection Method: Blood Draw

Specimen Type: Serum

Test Preparation: No preparation required

When and Why the Free T3 and Free T4 Blood Test Panel May Be Ordered

The Free T3 and Free T4 Blood Test Panel may be ordered when:

  1. Evaluating Thyroid Function: Especially when initial thyroid screening tests, such as the TSH test, indicate a potential problem.

  2. Monitoring Treatment: For those who are receiving thyroid hormone replacement or suppressive therapy.

  3. Symptoms of Thyroid Dysfunction: In individuals displaying signs of hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid), even if initial TSH tests are normal.

  4. Pregnancy: Particularly in pregnant women who have a history of thyroid disease, have had thyroid surgery, or have been exposed to radiation.

What the Free T3 and Free T4 Blood Test Panel Checks For

  • Free T3 (Triiodothyronine): This test measures the concentration of free T3 hormone in the blood. T3 is the more potent and active form of thyroid hormone, though it exists in smaller quantities than T4.

  • Free T4 (Thyroxine): This measures the amount of free T4 hormone in the blood. T4 is produced in greater amounts by the thyroid gland and is converted to T3 in the body's tissues.

Conditions or Diseases the Free T3 and Free T4 Blood Test Panel Can Check For

  • Hyperthyroidism: Elevated levels of free T3 and/or free T4 usually indicate an overactive thyroid. Common causes include Graves' disease, toxic multinodular goiter, or thyroiditis.

  • Hypothyroidism: Lowered levels of free T3 and/or free T4 suggest an underactive thyroid. Causes can include Hashimoto's thyroiditis, thyroid removal, or certain medications.

  • Non-thyroidal Illness: Sometimes, abnormalities in free T3 and free T4 levels can arise from non-thyroidal illnesses or conditions. It's crucial to differentiate this from genuine thyroid dysfunction.

The Free T3 and Free T4 Blood Test Panel is a crucial instrument in understanding the function of the thyroid gland and diagnosing potential disorders. By providing insight into the active thyroid hormone levels in the body, healthcare professionals can better diagnose, treat, and manage thyroid-related conditions.

We advise having your results reviewed by a licensed medical healthcare professional for proper interpretation of your results.

The following is a list of what is included in the item above. Click the test(s) below to view what biomarkers are measured along with an explanation of what the biomarker is measuring.

Also known as: Free T3, FT3, T3 Free

T3, Free

This test measures the amount of triiodothyronine, or T3, in the blood.

Also known as: Free T4, FT4, T4 Free

T4, Free

The free T4 test is not affected by protein levels. Since free T4 is the active form of thyroxine, the free T4 test is may be a more accurate reflection of thyroid hormone function.
*Process times are an estimate and are not guaranteed. The lab may need additional time due to weather, holidays, confirmation/repeat testing, or equipment maintenance.

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