LabCorp Test

Tri-iodothyronine (T3) Blood Test

Quick Overview

Ordered to help in evaluating thyroid gland function and in the diagnosis of hyperthyroidism.

Test #002188


Availability: In stock

Also Known As T3 Hormone; T3, Total; Total T3
Preparation No special preparation required.
Test Results 1-2 days. May take longer based on weather, holiday or lab delays.

A T3 blood test from Walk-In Lab helps evaluate thyroid gland function and in the diagnosis of hyperthyroidism.

The Tri-Iodothyronine blood test also goes by T3 Hormone, T3, Total and Total T3 is a particular hormone produced by the thyroid gland.  T3 is the active thyroid hormone which regulates metabolism by controlling the rate at which oxygen and calories are converted to energy in our cells.  It helps control the body's metabolism, temperature, and heart rate.

Potential thyroid disorders include:

  • hyperthyroidism: when your thyroid produces too much thyroid hormone
  • hypopituitarism: when your pituitary gland doesn’t produce normal amounts of pituitary hormones
  • primary or secondary hypothyroidism: when your thyroid doesn’t produce normal amounts of thyroid hormones
  • thyrotoxic periodic paralysis: when your thyroid produces high levels of thyroid hormones, resulting in muscle weakness

A thyroid disorder can cause a wide range of symptoms. For example, you might have mental issues such as anxiety, or physical problems such as constipation and menstrual irregularity.

Other possible symptoms include:

  • 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

If you already have confirmation of a thyroid problem, a T3 test is used to see whether there have been any changes in your condition.

Abnormally high levels of T3 are common in pregnant women and those with liver disease. If your T3 test also measured the free T3 level, your doctor may be able to rule out these conditions.

High T3 levels

If you’re not pregnant or suffering from liver disease, elevated T3 levels might indicate thyroid issues, such as:

  • Graves’ disease
  • hyperthyroidism
  • painless (silent) thyroiditis
  • thyrotoxic periodic paralysis
  • toxic nodular goiter

High T3 levels might also indicate high levels of protein in the blood. 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. It could also indicate that you have a long-term illness since T3 levels decrease when you’re sick. If you’re sick enough to be hospitalized, your T3 levels are likely to be low. This is one reason that doctors do not routinely use the T3 test as a thyroid test. Instead, they often use it along with the T4 and TSH test to get a more complete picture of how your thyroid is working.

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