If you want to understand what thyroxine and thyroxine tests are, check out these frequently asked questions.
In this article:
- What Is Thyroxine?
- How Is Thyroxine Controlled?
- What Happens If Thyroxine Is High?
- What Happens If Your Body Produces Too Little Thyroxine?
- What Is a Thyroxine Test?
- Why Do You Need to Take the Test?
- What Happens During a Thyroxine Test?
- Do You Need to Do Anything to Prepare for the Test?
- Are There Risks to a Thyroxine Test?
- What Do the Results of the Test Mean?
- Is There Anything Else You Must Know About the Test?
What You Should Know About Thyroxine and Its Test
What Is Thyroxine?
Thyroxine or T4 is a type of thyroid hormone that is released into the bloodstream by your thyroid gland. This hormone is an inactive form converted into an active one (triiodothyronine) by your organs like kidneys and liver. The hormones in your thyroid gland play an important role in regulating bone maintenance, brain development, muscle control, digestive and heart functions, and metabolic rate.
How Is Thyroxine Controlled?
A feedback loop system controls the production and release of the T4 hormone, which involves the thyroid and pituitary glands and the hypothalamus in the brain. The hypothalamus releases a thyrotropin-releasing hormone that triggers the pituitary gland to create a thyroid stimulating hormone, which stimulates the production of triiodothyronine and thyroxine in the thyroid gland.
This process regulates the production system of the hormones to prevent the release of the thyroid stimulating and thyrotropin-releasing hormones at the same time when levels of triiodothyronine and thyroxine increase. This allows your body to have good control over your thyroid hormone levels.
What Happens If Thyroxine Is High?
Thyrotoxicosis is a condition where your body releases high thyroxine levels into the bloodstream. This is caused by your thyroid gland’s overactivity (hyperthyroidism) that results in a benign tumor in your thyroid, inflammation of the thyroid, and Graves’ disease. Goiter is also another indication of thyrotoxicosis because of your thyroid gland’s enlargement. Other effects of thyrotoxicosis are the following:
- retraction of the eyelids (leading to a “staring” appearance)
- hair loss or thinning
- irregular or rapid heartbeat
- irregular menstrual cycle
- increased bowel movements
- increased appetite
- weight loss
- intolerance to heat
What Happens If Your Body Produces Too Little Thyroxine?
Hypothyroidism is when your body releases not enough thyroxine, which is caused by the use of certain drugs, poor iodine intake, and autoimmune diseases. If left untreated during childhood, hypothyroidism can lead to reduced growth and mental impairment. Other effects of this condition are as follows:
- reduced metabolism and fertility
- muscle stiffness
- poor memory
- reduced appetite
- weight gain
- low heart rate
- cold temperature intolerance
What Is a Thyroxine Test?
The thyroxine test aims to help diagnose thyroid gland disorders by measuring the level of thyroxine T4 in your blood. If there is too much or little of it, it may indicate thyroid disease. The total T4 test measures both free T4 (the hormone that enters the tissues when needed) and bound T4 (the hormone the attaches to proteins, preventing them from entering your tissues). Another test that is considered more accurate in monitoring your thyroid function is the free T4, which only measures this type of hormone.
Why Do You Need to Take the Test?
The primary reason for taking the thyroxine test is to check your thyroid function and know if you have thyroid disorders. Thyroid disease commonly occurs in women below 40 years old and often runs in the family. You may need to take the test if you have a family member that has had thyroid disease or if you experience symptoms of hyperthyroidism or hypothyroidism.
What Happens During a Thyroxine Test?
A thyroxine test is similar to taking any blood sample where a health professional takes a small amount of your blood using a needle and places the sample in a test tube to be taken to the lab for screening. It usually takes less than 5 minutes to complete the blood collection. If an infant is taking the test, the blood sample may be collected by puncturing the heel using a tiny needle.
Do You Need to Do Anything to Prepare for the Test?
Commonly, you don’t need to do anything to prepare before the test. If your physician needs more blood samples, you may be required to fast for several hours before the procedure to make sure your results are accurate.
Are There Risks to a Thyroxine Test?
The test is considered safe for the patient. You may only experience a slight pain when the needle enters your vein or bruising at the spot where the needle entered, both of which usually go away quickly. You may feel lightheaded or faint after having the blood drawn, especially if your physician needs more sample from you.
What Do the Results of the Test Mean?
Upon getting your results, you may see a free T4 index, free T4, or total T4 form. In the case of a free thyroxine index, you will see the comparison of the bound and free T4. High levels or low levels of any of these tests indicate hyperthyroidism or hypothyroidism, respectively. If your results are not normal, your doctor may require more thyroid tests to help them with the diagnosis:
- tests for Hashimoto’s disease, an autoimmune disease that leads to hypothyroidism
- tests for Grave’s disease, an autoimmune disease that leads to hyperthyroidism
- a thyroid stimulating hormone test
- a T3 thyroid hormone test
Is There Anything Else You Must Know About the Test?
There is a high risk of developing thyroid disease during pregnancy because the function of your thyroid gland changes, which typically is not significant. Some women can have thyroid disease during this time of their life (usually hyperthyroidism) primarily because of pregnancy hormones. Hypothyroidism may develop in less often cases.
If you develop thyroid disease during pregnancy, your doctor will continue monitoring your condition even after you give birth to your child. It’s best to consult with your doctor if you have a history of thyroid disease if you’re thinking of getting pregnant to make necessary medical changes.
Check out this quick video on the functions of thyroxine from Dr. Jamie Taft:
Now that you have a better understanding of what thyroxine is and what to expect from the test, you can assess whether you need to take the test or not. The function of your thyroid hormones may be unpredictable, especially when you’re pregnant, but it’s still best to consult your doctor if you experience any effects of an abnormal thyroid. Know the medical history of your family now and take necessary actions when you think it’s needed.
What other facts about T4 and the T4 test can you share with us? Leave them in the comments section.
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