FT4-Free Thyroxine Serum Test

Free T4 test is done along with TSH to
1. Diagnose thyroid disorders both overt & subclinical
2. Monitoring patients on thyroid replacement therapy
In a very small group of patients only T3 & FT3 is increased.
In pregnancy due to increase in thyroglobulin and decrease in albumin may cause increase of T3 & T4 levels, without actually impacting body functions hence testing FT3 and FT4 is more representative

Free T4 test measures levels of FT4 hormone in blood

Free T4 test requires a blood sample. A tourniquet (elastic) band is placed tightly on the upper arm. The patient is then asked to make a fist. This helps in the build-up of blood filling the veins. The skin is disinfected before needle insertion and the blood sample is collected in vacutainer.

High TSH & high T3/FT3 and T4/FT4: Thyroxine replacement therapy; pituitary adenoma; drugs like heparin, amiodarone, beta blockers, steroids; neonates; resistance to thyroid hormones
High TSH & low T3/FT3 and  T4/FT4: Autoimmune thyroiditis, thyroidectomy, post-radiation, iodine deficiency, thyroid infiltrating tumour/ amyloid
Low TSH & Low T3/FT3 and T4/FT4: Central hypothyroidism, non-thyroidal illness
Low TSH & High T3/FT3 and FT4: Grave's disease, toxic multinodular goitre, toxic adenoma, thyroiditis, drugs, hyperemesis gravidarum & hydatiform mole, congenital hyperthyroidism

In most cases, no special preparation is required for this test. Make sure to inform your healthcare professional about any medicines or supplements you are taking as they can affect the results of the test.

There is little to no risk associated with a T4-Free Thyroxine test. You may experience slight pain or bruising at the injection site, but the symptoms disappear fast.

If you have taken a T4-Free Thyroxine test, the results will be reported as free T4. T4 levels lower than normal can indicate hypothyroidism, thyroiditis, or congenital hypothyroidism. On the other hand, higher than normal free T4 levels can be a sign of hyperthyroidism, thyroiditis, toxin thyroid nodule, toxic goitre, or a non-cancerous tumour in the pituitary gland.

Certain medications like phenobarbital can have an impact on your free T4 levels. Besides this, severe cases of chronic ailments such as cirrhosis of the liver or chronic renal failure can also affect your T4-Free Thyroxine test results.

The normal range for free T4 ranges between 0.9 and 2.3 nanograms per decilitre, or 12 to 30 picomoles per litre. However, the normal value ranges may differ slightly depending on the laboratory where you get your test done.

The normal range for free T4 classified according to age are as follows:

o   Children/adolescents: 0.8-2 ng/dL

o   Adults: 0.7-1.8 ng/dL

o   Pregnant women: 0.5-1 ng/dL

Normal TSH with normal T4 indicates normal thyroid function. However, high TSH along with a normal T4 means we are at a higher risk of developing underactive thyroid. On the contrary, low TSH levels with high T4 levels mean that our thyroid gland is overactive.

Your healthcare provider may recommend you to get a T4-Free Thyroxine serum test if you show any signs of thyroid disorder, such as:

• Symptoms of underactive thyroid
• Symptoms of overactive thyroid
• Abnormal findings in other types of thyroid tests, like T3 or TSH
• Hypopituitarism – a condition where the pituitary gland fails to produce enough hormones
• Nodule or Lump in the thyroid gland
• An irregular or enlarged thyroid gland
• Problems getting pregnant

Thyroid disorder is a hereditary condition. Therefore, your doctor may prescribe you a T4 test in case anyone in your family has a thyroid disorder. You may also require a T4 test if you show any symptoms of too little or too much thyroid hormone.

Common symptoms of hypothyroidism include:

• Weight gain
• Fatigue
• Dry, thinning hair
• Dry skin
• Over-sensitivity to cold temperatures
• Heavy menstrual periods or fertility issues
• Depression
• Slow heart rate

Symptoms of hyperthyroidism include:

• Nervousness, irritability, and anxiety
• Weight loss
• Muscle weakness
• Shaky hands
• Over sensitivity of heat
• Arrhythmia
• Goiter
• Frequent bowel movements
• Fatigue and trouble sleeping

o   Free thyroxine

o   Free T4

o   Thyroxine screen

The FT4 test is a blood test that assesses the amount of free thyroxine (T4) in the bloodstream. This is the active form of the hormone that is not bound to proteins and is ready for immediate use by the body's tissues.

The FT4 test is essential for diagnosing and monitoring thyroid disorders such as hypothyroidism and hyperthyroidism. It provides accurate information about the active form of thyroxine available to the body, crucial for managing thyroid health and metabolic function.

T3 stands for triiodothyronine, while T4 represents thyroxine. These are the two main hormones produced by the thyroid gland.

TSH stimulates the thyroid gland to produce T4, which is then converted into the more active form, T3. The levels of T3 and T4 in the blood provide feedback to the pituitary gland to adjust TSH production, maintaining a balance in thyroid hormone levels.

Yes, the Free T4 Test can be taken during pregnancy. However, it is important to inform your healthcare provider about the pregnancy, as it can affect the test results and their interpretation. 

A low FT4 level may indicate hypothyroidism, which can cause symptoms such as weight gain, fatigue, dry skin, sensitivity to cold, and other metabolic disturbances.

If your FT4 levels are high, indicating hyperthyroidism, treatment may involve medications to reduce thyroid hormone production, radioactive iodine, or surgical removal of part or all of the thyroid gland, depending on the underlying cause and severity.

The FT4 test can be performed at any age, including newborns, to screen for congenital hypothyroidism and in adults to diagnose and monitor thyroid disorders.

The benefits of the FT4 blood test include accurate diagnosis and monitoring of thyroid disorders, differentiating between primary and secondary thyroid issues, and guiding treatment decisions to ensure optimal thyroid function.

No, fasting is generally not required before taking the FT4 test. However, inform your healthcare provider about any medications or supplements you are taking, as some may affect the test results.

Metropolis Healthcare provides a hassle-free home sample collection service for the FT4 test. A trained phlebotomist will visit your home to collect the sample, ensuring both comfort and safety. With strict adherence to sample handling standards, you can rely on Metropolis for accurate and dependable FT4 test results.

Typically, results for FT4 test are available after 6 hours, depending on the day/time the sample was collected and processed.