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The free thyroxine test (FT4) is often called the free T4 test, and it analyses the amount of free thyroxine in the blood. Thyroxine (T4) circulates in the blood in two forms: free form (FT4) and bound form. Thyroxine (T4) is a hormone secreted by the thyroid gland and is very essential for growth and metabolism. The FT4 test helps to diagnose any suspected thyroid disease (hypothyroidism or hyperthyroidism) and to determine the treatment efficiency in people who have been diagnosed with a thyroid condition.
The higher values could indicate an overactive thyroid (hyperthyroidism) and show symptoms like excessive appetite, anxiety, heart palpitations, sweating, shortness of breath, and weight loss. Abnormally low thyroxine values lead to hypothyroidism and cause symptoms like weakness, cold intolerance, weight gain, and dry skin.
The other names are FT4, Free Thyroxine, and Thyroxine Free Test.
There is only one parameter.
Thyroxine (T4) is one of the two important hormones that are produced by the thyroid gland, a small butterfly-shaped organ that lies flat across the windpipe at the base of the throat. The other major thyroid hormone is called triiodothyronine (T3), and together they help to control the rate at which the body uses energy. Almost all the T4 and T3 found in the blood are bound to the protein. And the rest is free (unbound) and is the biologically active form of the hormone. This test analyses the amount of free T4 in the blood.
Most of the thyroid hormone that is produced by the thyroid is T4. This hormone is relatively inactive, but it is converted into the much more active T3 in the liver and other tissues in the body.
Thyroxine (T4) levels are regulated by the feedback system that the body uses to maintain a stable amount of thyroid hormones in the blood. T3 and thyroid stimulating hormone (TSH), along with the regulatory hormone, the thyrotropin-releasing hormone (TRH), that comes from the hypothalamus, is also a part of the feedback system.
When thyroid hormone levels decrease in the blood, the pituitary gland produces thyroid stimulating hormone (TSH) in response to TRH stimulation. Thyroid-stimulating hormone (TSH) in turn stimulates the thyroid by binding to the TSH receptor to produce and release T4 and T3.
When thyroid hormone levels increase in the blood, the pituitary gland manufactures less TSH and the thyroid produces less T4 and T3.
Usually, when all three organs (hypothalamus, pituitary, and thyroid) are functioning normally, thyroid production is regulated to maintain relatively stable levels of thyroid hormones in the blood.
If the thyroid gland does not produce enough T4 and T3 (underactive thyroid) due to thyroid dysfunction or insufficient TSH, then the affected person experiences the symptoms of hypothyroidism such as weight gain, dry skin, cold intolerance, irregular menstruation, and fatigue. Hashimoto thyroiditis is the most common condition or cause of hypothyroidism.
If the thyroid gland produces too much T4 and T3, the affected person might experience symptoms associated with an overactive thyroid (hyperthyroidism), such as rapid heart rate, anxiety, weight loss, difficulty sleeping, tremors in the hands, and puffiness around dry, irritated eyes, and, in some cases, bulging eyes. Usually, Graves' disease is the common cause of hyperthyroidism.
Both hyperthyroidism and hypothyroidism may also be caused by thyroiditis, thyroid cancer, and excessive or deficient production of TSH. The effect of these conditions on thyroid hormone production may be detected and monitored by analysing the free T4.
A free T4 test is recommended when a person has any symptoms of hyperthyroidism or hypothyroidism and or when a person has an enlarged thyroid gland (goiter) or thyroid nodule, particularly when the TSH test is abnormally out of range.
Signs and symptoms of hyperthyroidism might include
Increased heart rate
Difficulty in sleeping
Tremors in the hands
Light sensitivity and visual disturbances
There can be puffiness around the eyes along with dryness, irritation, and, in some cases, bulging of the eyes.
Menstrual irregularities in women
Signs and symptoms of hypothyroidism may include
Free T4 testing can be ordered along with other thyroid tests on a regular basis when a person is undergoing treatment for a thyroid disorder.
In pregnant women with known thyroid disorders, the doctor is likely to recommend thyroid testing early and late in the pregnancy and for a time period following delivery to evaluate the mother and baby.
No special preparation is required and fasting is not required.
This test requires a blood sample.
A healthcare provider, who is also called a phlebotomist, usually performs blood draws, including those for a Free T4 test, but any healthcare provider trained in drawing blood can perform this task. These samples are sent to a lab where a medical laboratory scientist prepares the samples and performs the tests on analysers or manually.
You may expect to experience the following during the blood test or a blood draw:
You have to sit comfortably on the chair, and a healthcare provider will check your arms for an easily accessible vein. It is the inner part of your arm on the other side of your elbow.
Once the phlebotomist has located a vein, they will clean and disinfect the area with an alcohol swab.
They will insert a needle into your vein to draw a blood sample. They may feel like a small pinch.
After they insert the needle, the required amount of blood is drawn into a test tube.
When they have drawn enough blood for the test, they’ll remove the needle and hold a cotton ball or gauze on the pricked site to stop any bleeding.
They will apply a band-aid over the pricked site, and the blood collection is finished.
This process takes less than five minutes.
Once the phlebotomist has collected the blood sample, it will be sent to the laboratory for processing or testing. When the reports are ready, your healthcare provider will share the results with you.
These blood tests are very common, and they don’t carry any significant risks. You can have a slight pain like an ant bite when the needle gets inserted, and a small bruise might develop there.
This report is available via email or WhatsApp within 6 hours of the collection of the blood sample.
The T4 level is reported either in nanograms per decilitre (ng/dL) or picomoles per litre (pmol/L). The reference range, or what is considered normal for T4, can vary slightly from laboratory to laboratory.
The results can be described as free T4 or free thyroxine index (FTI). Free thyroxine index (FTI) means the test result was calculated by using a formula that compares to the total T4 and some estimation of the level of thyroid hormone proteins.
If the doctor is testing the free T4 to diagnose or rule out a thyroid or pituitary gland disorder, the test results will be considered along with the TSH. The following table demonstrates typical patterns found in these disorders:
Normal ranges might vary slightly among different laboratories. Some of the labs use different measurements or might test different samples. Speak to your health care provider about the meaning of your specific test results.
Thyroid Function Test, Thyroid Function Test Free, Thyroid peroxidase (TPO)
How do I book a Free T4 (FT4) test at home?
Log on to www.orangehealth.in and submit your details. Our highly trained, professional, and vaccinated eMedics will be at your doorstep within 60 minutes or at the time booked by you.
Frequently Asked Questions on FT4 Test
A free T4 (FT4) test is used to find out how well your thyroid gland is working. T4 is one of the two hormones (T3 and TSH) produced by the thyroid gland.
Increased free T4 levels might indicate hyperthyroidism, thyroid hormone resistance syndrome, or T4 toxicosis. Elevated free T4 can cause symptoms of hyperthyroidism, including excessive appetite, anxiety, heart palpitations, sweating, shortness of breath, weight loss, and intolerance to heat.
Some of the early warning signs of thyroid problems include fatigue, hair loss, weight loss, weight gain, slowed heart rate, increased heart rate, sensitivity to heat, and sensitivity to cold.
A normal range is 0.78–2.19 nanograms per decilitre(ng/dL). Normal ranges might slightly vary from lab to lab.