Triiodothyronine (T3) Lab Values

Join to watch the full lesson now.

Included In This Lesson

Study Tools



Determine the significance and clinical use of measuring T3 in clinical practice


Lab Test Name:




T3 – Triiodothyronine is one of two thyroid hormones present in the bloodstream. It contributes to metabolism, digestive function, muscle control, brain development and function, cardiac function and maintenance of bone. T3 is able to impact cells in the body as it is the active form of thyroid hormone. The liver and kidneys convert most of the prohormone, Thyroxine or T4, to T3, the more biological active thyroid hormone that binds to the Thyroid hormone receptors and triggers most of the biological effects.


T3 – Triiodothyronine

  • Active form of thyroid hormone
  • Converted to T3 from T4 in liver and kidneys
  • Contributes to:
    • Metabolism
    • muscle control 
    • Cardiac function
    • brain development and function
    • Bone maintenance




  • Hyper- and hypothyroidism
    • Diagnose
    • Evaluate function
    • Monitor therapy
  • Hypopituitarism


Normal Therapeutic Values:

Normal – 

  • 80 to 180 ng/dL


  • Serum separator tube

What would cause increased levels?

Elevated T3:

  • Hyperthyroidism
    • Graves’ disease
    • Thyroid nodules/inflammation
  • Medications
    • Birth control
    • Methadone
    • Estrogen replacement


What would cause decreased levels?

Decreased T3:

  • Hypothyroidism
    • Underactive thyroid
    • Antithyroid medications
  • Severe illness
  • Medications that lower T4- leads to decreased T3
    • Amiodarone
    • Androgens
    • Lithium
    • Anabolic steroids
    • Phenytoin
    • Propranolol
Join to watch the full lesson now.


Hey everyone. This is Abby with In this lesson, we’re going to talk about T3, the thyroid hormone. It’s also called triiodothyronine. We’ll talk about normal values, increased values and decreased values. You know we’re gonna be talking about hyper and hypothyroidism don’t you? Let’s get started. 


A lab to measure triiodothyronine, or T3, is to evaluate the function of the thyroid gland. T3 is produced by the thyroid, along with T4, and it’s actually the active form. So, when T4 gets into circulation, it actually needs to be converted into T3 in the liver and kidneys and other tissues. What these thyroid hormones do, or how they work within the body, is that they contribute to metabolism, muscle control, cardiac function, brain development and function, and also bone maintenance. Pretty important, little butterfly-shaped gland here in the throat. 


Some clinical indications for why this lab would be drawn are to evaluate and diagnose hyper and hypothyroidism. It’s also used to monitor to see if therapy’s working. It can also be used to monitor or look at the functionality of our pituitary gland, particularly in hypopituitarism. That means that there’s a lack of TSH, and if there’s not enough TSH, is there going to be enough T3, T4, probably not, right? We remember how hormones work. 


Normal therapeutic values are between 80 and 180 nanograms per deciliter. We’ll see this specimen collected in a serum separator tube. Values will be increased in the case of hyperthyroidism. We see that with graves’ disease. Also, in the case of thyroid nodules or inflammation. Certain medications like birth control, methadone, and even estrogen replacement can affect our T3 values and drive them up. They’ll be decreased in the case of hypothyroidism or an underactive thyroid. Also, we can see it suppressed in antithyroid medications used for hyperthyroidism. Also, in the case of severe illness, we’ll have a decrease in the production of T3. Now, medications actually lower T4 values, which then of course, because T4 becomes T3,  we see it as a decrease in T3 as well. That would be the case with medications like amiodarone, androgens, lithium, anabolic steroids, phenytoin, and propranolol.


Linchpins for this lesson, for triiodothyronine, took me a long time to figure out how to pronounce it, are that this is one of the thyroid hormones, and it contributes largely to metabolism and functionality of many body systems, but it primarily measures thyroid function. Normal values are between 80 to 180 nanograms per deciliter. When values are increased, hyperthyroidism, when they’re decreased hypothyroidism. 


This wraps up our lesson on T3. You all did great. Remember, we know you can do it. We love you, now go out and be your best self today and always, happy nursing.


Join to watch the full lesson now.