LabCorp Test

Thyroxine (T4) Blood Test

Quick Overview

Thyroid function test.

Test #001149


Availability: In stock

Also Known As T4 Total; Tetraiodothyronine
Preparation No fasting required. Stop biotin consumption at least 72 hours prior to the collection.
Test Results 1-2 days. May take longer based on weather, holiday or lab delays.

The Thyroxine (T4) Blood Test from Walk-In Lab is a thyroid function test. It measures the level of thyroxine in the blood, helping to diagnose thyroid disorders such as hyperthyroidism and hypothyroidism. 

This test is for individuals who have symptoms of either an underactive or an overactive thyroid and want to assess whether their thyroid is producing too much or too little thyroxine. It can also be used to monitor an already diagnosed thyroid disorder.

T4 blood test assesses thyroid function by measuring the level of thyroxine in the blood. This hormone plays a role in several of your body’s functions, including growth and metabolism.  Decreased levels of T4 are typically found in hypothyroidism and in the third stage of (painful) subacute thyroiditis. Increased T4 is associated with hyperthyroidism, subacute thyroiditis in its first stage, and with thyrotoxicosis due to Hashimoto disease. A Thyroxine blood test can also be used to diagnose T4 toxicosis. Increased thyroxine can be caused by excessive intake of iodine or with surreptitious use of thyroxine. Further, T4 levels may be abnormal in the presence of systemic nonthyroidal disease.

If a thyroid-stimulating hormone (TSH) test has come back with abnormal results. A T4 test will help etermine what is wrong with your thyroid.

Some thyroid disorders include:

  • hyperthyroidism (overactive thyroid)
  • hypothyroidism (underactive thyroid)
  • hypopituitarism (underactive pituitary gland)
  • thyrotoxic periodic paralysis (occasional muscle weakness caused by high levels of thyroid hormone)

Symptoms of thyroid disorders include:

  • eye issues, such as dryness, irritation, puffiness, and bulging
  • skin dryness or puffiness
  • hair loss
  • hand tremors
  • increased heart rate

You may also experience more general symptoms such as:

  • weight changes
  • difficulty sleeping or insomnia
  • anxiety
  • fatigue and weakness
  • intolerance to cold
  • sensitivity to light
  • menstrual irregularity

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