What is the Difference Between T3 T4 TSH and FT3 FT4 TSH

The key difference between T3 T4 TSH and FT3 FT4 TSH is that T3 T4 TSH is a thyroid hormone test that measures the level of hormones bound to thyroxine-binding globulin in serum, while FT3 FT4 TSH is a thyroid hormone test that measures the level of hormones unbound to thyroxine-binding globulin in serum.

Thyroid tests indicate the level of performance of the thyroid gland since it is an important aspect with reference to human metabolism. The thyroid gland produces different types of hormones, such as thyroxine (T3) and triiodothyronine (T4). TSH, or thyroid-stimulating hormone, is a type of pituitary hormone that regulates the release of hormones from the thyroid gland. These hormones get classified into two groups based on the attachment to a protein in serum: unbound T3 and T4 are free T3 (FT3) and free T4 (FT4).

CONTENTS

1. Overview and Key Difference
2. What is T3 T4 TSH
3. What is FT3 FT4 TSH
4. Similarities – T3 T4 TSH and FT3 FT4 TSH
5. T3 T4 TSH and FT3 FT4 TSH in Tabular Form
6. Summary – T3 T4 TSH vs FT3 FT4 TSH

What is T3 T4 TSH?

T3 T4 TSH is a type of hormone test to check the function of the thyroid gland through analysis of levels of bound thyroxine and triiodothyronine hormone to thyroxine-binding globulin in serum. The thyroid gland is a small butterfly-shaped gland that regulates most of the metabolic activities in humans. The thyroid gland secretes two types of hormones: thyroxine (T4) and triiodothyronine (T3). These hormones function together in regulating metabolic activities of the body. TSH or thyroid-stimulating hormone secreted by the pituitary gland, stimulates the thyroid gland to secrete T3 and T4 hormones. These hormones are attached to thyroxine-binding globulins.

During a test to evaluate the function of the thyroid gland, along with T3 T4, TSH level is also tested. This test is required when an individual develops symptoms of hyperthyroidism. These symptoms include weight loss, anxiety, fatigue, low tolerance for heat, increased heart rate, etc. If the test results indicate higher T3 levels, it is a direct sign of hyperthyroidism. T3 test results are often compared with T4 and TSH test results to identify other types of diseases related to the thyroid gland. The normal ranges of T3 T4 TSH test results are T4 5.0 – 11.0 ug/dL (micrograms per deciliter of blood), T3 100 – 200 ng/dL (nanograms per deciliter of blood), and TSH 0.5 to 5.0 mIU/L (milliunits per liter) in adults.

What is FT3 FT4 TSH?

FT3 FT4 TSH is a type of hormone test to check the function of the thyroid gland through the analysis of levels of free thyroxine and triiodothyronine hormone in serum. Unbound T3 T4 hormones to thyroxine-binding globulin are free T3 (FT3) and free T4 (FT4). Along with FT3 and FT4, TSH level is also analyzed to identify potential disorders related to the thyroid gland as a frontline investigator.

The test FT3 FT4 TSH analyzes the free T3 and T4 circulating in blood along with TSH. This test is important to measure the amount of free thyroxine and triiodothyronine circulating in the blood. In some instances, FT3 FT4 TSH results could be misleading in patients with non-thyroidal illness if the patient is undergoing acute illness. Hence, the FT3 FT4 TSH test needs to be delayed for at least three months post-acute illness. This test has to be conducted immediately if a healthy individual develops symptoms like fatigue, tremors in hand, sleeping troubles, frequent bowel movements, etc. The normal levels of FT3 is 2.3 – 4.1 pg/mL (picograms per milliliter of blood), FT4 is 0.9 – 1.7 ng/dL (nanograms per deciliter of blood) and TSH 0.5 to 5.0 mIU/L (milliunits per liter) in adults.

What are the Similarities Between T3 T4 TSH and FT3 FT4 TSH?

• T3 T4 TSH and FT3 FT4 TSH are two types of thyroid tests.
• Both tests are based on the hormones related to the thyroid gland.
• Both T3 T4 TSH and FT3 FT4 TSH identify potential diseases related to the thyroid gland.
• They are important to diagnose hyperthyroidism.
• The tests are frequently used by many medical practitioners.

What is the Difference Between T3 T4 TSH and FT3 FT4 TSH?

T3 T4 TSH is a thyroid hormone test that measures the level of hormones bound to thyroxine-binding globulin in serum, while FT3 FT4 TSH is a thyroid hormone test that measures the level of hormones unbound to thyroxine-binding globulin in serum. Thus, this is the key difference between T3 T4 TSH and FT3 FT4 TSH. The normal range lies between T4 5.0 – 11.0 ug/dL, T3 100 – 200 ng/dL and TSH 0.5 to 5.0 mIU/L in adults in T3 T4 TSH. Normal range lies between FT3 2.3 – 4.1 pg/mL, FT4 0.9 – 1.7 ng/dL and TSH 0.5 to 5.0 mIU/L in adults in FT3 FT4 TSH.

The below infographic presents the differences between T3 T4 TSH and FT3 FT4 TSH in tabular form for side by side comparison.

Summary – T3 T4 TSH vs FT3 FT4 TSH

The thyroid gland produces different types of hormones, such as thyroxine (T3) and triiodothyronine (T4). TSH is a type of pituitary hormone that regulates the release of hormones from the thyroid gland. The key difference between T3 T4 TSH and FT3 FT4 TSH is that T3 T4 TSH is a thyroid hormone test that measures the level of hormones bound to thyroxine-binding globulin in serum, while FT3 FT4 TSH is a thyroid hormone test that measures the level of hormones unbound to thyroxine-binding globulin in serum. Many medical practitioners frequently use both tests to assess common symptoms to diagnose hyperthyroidism and to identify potential diseases related to the thyroid gland.

Reference:

1. “Thyroid Blood Tests.” Cleveland Clinic.
2. “Triiodothyronine (T3) Tests: Medlineplus Medical Test.” MedlinePlus, U.S. National Library of Medicine.

Image Courtesy:

1. “Hypothyroidism disease” By purple carrot nutrition – (CC BY-SA 4.0) via Commons Wikimedia
2. “Figure 37 04 01” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia