Test Detail
Understanding the Test
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Content created by
Written by
Dr. Shreya Gupta
BDS, MDS - Oral and Maxillofacial Pathology
Reviewed by
Dr. Ashish Ranjan
MBBS, MD (Pharmacology)
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T4 Free & TSH, Ultrasensitive.

You need to provide
This test is for
Male, Female
Test Preparation
  1. Sample to be given at the same time of the day in follow-up cases.
  2. It is advisable to stop multivitamins or dietary supplements containing biotin (vitamin B7) for at least 2 days before the test.
  3. You need not stop taking your thyroid medications on the day of the test unless otherwise advised by the doctor.

Understanding T4 Free & TSH, Ultrasensitive.

What is T4 Free & TSH, Ultrasensitive.?

A T4 Free & TSH, Ultrasensitive. test measures the amount of free form of thyroxine (T4 Free or FT4) and thyroid stimulating hormone (TSH) in the blood. This test helps evaluate how well your thyroid gland works and detects possible thyroid disorders, including hyperthyroidism (too much thyroid hormones) and hypothyroidism (inadequate secretion of thyroid hormones).

Thyroid-stimulating hormone (TSH), also known as thyrotropin, is produced by the pituitary gland present in the brain. TSH stimulates the thyroid gland to release thyroid hormones triiodothyronine (T3) and thyroxine (T4). Together, TSH, T3 & T4 hormones play a vital role in controlling how your body uses and stores energy and maintaining body weight and temperature. 

T3 and T4 hormones exist in the blood in two forms: bound (attached to transport proteins) and free (not attached to proteins and can enter and affect the body tissues). The T4 Free & TSH, Ultrasensitive. test measures the free form of T4 (FT4), a more accurate indicator of thyroid gland function than the bound form T4.

Your doctor may advise a T4 Free & TSH, Ultrasensitive. test if you show symptoms suggestive of hyperthyroidism, such as increased appetite, weight loss, sweating, anxiety, tremors, etc., or hypothyroidism, such as fatigue, weight gain, dry skin, constipation, etc. This test is also recommended for women during pregnancy to check if they have adequate amounts of thyroid hormones, as these hormones are necessary for the healthy development of babies.

Abnormal levels of FT4 or TSH may indicate thyroid dysfunction (Hyperthyroidism or hypothyroidism), with high or low levels suggesting different types of thyroid disorders, such as goiter, Graves’ disease, or Hashimoto’s thyroiditis.

No special preparations are needed for this test. Usually, you do not need to stop taking your thyroid medication before taking this test. However, inform your doctor about all your medicines, as some can affect thyroid function. Biotin (Vitamin B7) is a commonly taken over-the-counter supplement that can lead to some aberrancy in your thyroid function tests even when the values are normal. Avoid taking biotin 2 days before a thyroid function test.

Test result ranges are approximate and may differ slightly between labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific results. The test results will help them determine your medical condition, make recommendations for lifestyle modifications such as diet and exercise, evaluate whether or not medication will be required to manage your condition, and formulate an overall treatment plan.

What is T4 Free & TSH, Ultrasensitive. used for?

A T4 Free & TSH, Ultrasensitive. test is done:

  • As part of routine health checkups to monitor your overall health.

  • To evaluate symptoms suggestive of an imbalance in thyroid hormone levels, such as fatigue, weight loss, hair loss, and changes to heart rate.

  • To diagnose and monitor the treatment of any suspected thyroid disease, such as hypothyroidism, hyperthyroidism, Grave’s disease, thyroiditis, or Hashimoto’s disease.

  • To detect an underactive thyroid gland in newborn babies.

  • To evaluate other disorders, such as thyroid nodules, goiters, and pituitary or hypothalamus gland disorders.

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about T4 Free & TSH, Ultrasensitive.

Frequently Asked Questions about T4 Free & TSH, Ultrasensitive.

Q. Why is a free T4 and TSH test done?

A free T4 and TSH test is done to check for hyperthyroidism or hypothyroidism when you are suspected of symptoms like weight gain/loss, fatigue, dry skin, hair thinning, slow heart rate, muscle weakness, anxiety, trouble sleeping, or frequent bowel movement.

Q. Can I take a free T4 and TSH test during pregnancy?

Yes, you can take a free T4 and TSH test during pregnancy. This test, along with others, is usually recommended during pregnancy to measure the levels of thyroid hormones, as thyroid disorders can complicate pregnancy.

Q. Is fasting required for a free T4 and TSH test?

No, fasting is not needed before taking this test. However, your doctor will guide you if any special preparation is required.

Q. What factors can lead to a variation in thyroid hormone levels?

TSH levels may show marked variation depending on the time when they are measured. So, daytime testing is usually preferred. Elevated TSH levels have also been observed with aging and during the cold winter months. Total T3 & T4 concentrations are also altered by changes in thyroid-binding protein levels. In such cases, levels of free-form T4 and T3 may be preferred.

Q. Is there any risk associated with this test?

There is usually no risk associated with this test. However, some people may feel a slight sting while the needle is pricked and may experience some bleeding that is normal and usually not bothersome. Some people may rarely experience slight swelling or bruising at the site of the needle prick. Applying ice 3-4 times daily for about a week may help reduce swelling and bruising. If it does not get better, consult your doctor.

Q. What is Hypothyroidism?

Hypothyroidism (underactive thyroid gland) is a condition in which the thyroid gland does not produce enough thyroid hormones. It can be commonly caused by intake of a low iodine diet or Hashimoto's thyroiditis (an autoimmune disease). Less common causes include previous treatment with radioactive iodine, injury to the pituitary gland (secretes TSH), intake of certain medicines, previous thyroid surgery, or a lack of a functioning thyroid gland at birth.

Q. What are the symptoms of hypothyroidism?

Symptoms of hypothyroidism include tiredness (fatigue), hoarseness, constipation, feeling cold, dry skin, dry and thin hair, puffy face, weight gain, and muscle weakness. Along with that, one may experience decreased sweating, depression, slowed heart rate, increased blood cholesterol levels, pain, and stiffness in your joints, impaired memory, problems of infertility or menstrual changes, muscle stiffness, aches, and tenderness.

Q. What is Hyperthyroidism?

Hyperthyroidism (overactive thyroid gland) is a condition in which there is an increased production of thyroid hormones by the thyroid gland. Causes of Hyperthyroidism include Graves’ disease, multinodular goiter, thyroid nodules, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. Diagnosis of this condition can help to relieve the symptoms and prevent long-term complications.

Q. What are the symptoms of hyperthyroidism?

Symptoms of hyperthyroidism include rapid heartbeat, palpitations, sudden weight loss, nervousness, anxiety, irritability, tremors (usually a fine trembling in your hands and fingers), changes in menstrual patterns, increased sensitivity towards heat, changes in bowel patterns (especially more frequent bowel movements), an enlarged thyroid gland (goiter) which may appear as a swelling at the base of your neck, increased appetite, sweating, fatigue, muscle weakness, sleep disturbances, skin thinning, fine and brittle hair.
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