T3 Test: Purpose, Preparation, Procedure and Results

Most of the T3 in your body binds to protein. Free T3 are the T3 that are not bind to protein and circulates in your blood. T3 total test is done to measures both kinds of T3 in your blood.

Updated: June 16, 2022

Thyroid is a small butterfly shaped gland that is located in the lower-front part of your neck that typically produces three hormones namely triiodothyronine (T3), thyroxine (T4), and calcitonin.
The thyroid produces T3 and T4 hormones when the pituitary gland releases TSH in the blood. Thyroid-stimulating hormone or TSH is responsible for regulation of metabolism, release of hormones by the thyroid gland, energy generation, heart rate and mood. Most of the T3 in your body binds to protein. Free T3 are the T3 that are not bind to protein and circulates in your blood. T3 total test is done to measures both kinds of T3 in your blood.
If T4 tests and TSH tests suggest hyperthyroidism or if you are showing signs of an overactive thyroid gland and your T4 and TSH are not elevated, a T3 test is suggested.
The normal range for the T3 is 100 to 200 ng/dL(nanograms of hormone per deciliter of blood). Abnormally high levels of T3 is an indication of a condition called Grave's disease which is an autoimmune disorder associated with hyperthyroidism.

Purpose of T3 Tests:

If any of the below thyroid disorders are suspected, a T3 test must me done.

  • When your thyroid gland produces too much thyroid hormone or hyperthyroidism
  • When your pituitary gland does not produce normal amounts of pituitary hormones or hypopituitarism
  • When your thyroid gland does not produce normal amounts of thyroid hormones known as primary or secondary hypothyroidism
  • When your thyroid gland produces high levels of thyroid hormones, resulting in muscle weakness known as thyrotoxic periodic paralysis.

A thyroid disorder can cause several symptoms which include:

  • anxiety
  • weakness and fatigue
  • difficulty sleeping
  • increased sensitivity to heat or cold
  • weight loss or gain
  • dry or puffy skin
  • dry, irritated, puffy, or bulging eyes
  • hair loss
  • hand tremors
  • increased heart rate
  • constipation
  • menstrual irregularity

Preparing for a T3 test:

Certain medications such as birth control pills or other medications containing hormones, such as androgens and estrogens, steroids or thyroid-related drugs may affect your T3 levels. Therefore before going for a T3 test your doctor should know about your medications in advance, so that they can advise you to temporarily stop using them or consider their effect when interpreting your results.

Procedure for a T3 Test:

A band will be tied by a technician around your arm so that the veins of the hand are more prominent to prick the injection. The vein is punctured with a fresh, disposable syringe and the blood is withdrawn after the site is cleaned with an alcohol swab. A cotton swab will be given to you after drawing the blood to place on the place where the injection was pricked. You will be asked to apply pressure on the cotton in order to stop the bleeding.
You might notice a bruise in the place where the injection was pricked on your skin. This is normal and should fade away in a few days. But if you experience unbearable pain, or if the area around the puncture becomes red and swollen, immediately follow up with your doctor. These could be signs of an infection.

Understanding the Results of a T3 test:

The normal range for the T3 is 100 to 200 ng/dL(nanograms of hormone per deciliter of blood). If the T3 results are normal, a T4 and TSH test along with T3 test can help your doctor figure out if you have a thyroid problem despite a normal T3 result.

High T3 levels:

Abnormally high levels of T3 are common in pregnant women and people with liver disease. Free T3 level, may be able to rule out these conditions. But if you are not pregnant or not suffering from liver disease, elevated T3 levels might indicate thyroid issues, such as:

  • hyperthyroidism
  • Grave's disease
  • painless thyroiditis
  • thyrotoxic periodic paralysis
  • toxic nodular goiter

High levels of protein in the blood may be a cause of high T3 levels. In rare cases, these elevated levels could indicate thyroid cancer or thyrotoxicosis.

Low T3 levels:

Abnormally low levels of T3 may indicate hypothyroidism or starvation. Because T3 levels decreases when you are sick, low levels could also indicate that you have a long-term illness. This is why a single test of T3 may not be able to figure out thyroid issues. However, abnormal results can help diagnosing in the right direction. A T4 or TSH test is advised to obtain a clearer picture of your thyroid function.


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