T4 Thyroxine Blood Tests near


T4 Test

Thyroxine (T4) is a hormone produced by the thyroid gland. The thyroid is a butterfly-shaped gland that lies below your Adam’s apple in the front of the neck. The gland is responsible for the production of the triiodothyronine (T3) and thyroxine (T4) hormones, which regulate your body’s metabolism and growth. T4 tests are used to determine the levels of the thyroxine hormone you have in your body. Too much or too little T4 can indicate a problem with your thyroid gland such as hyperthyroidism or hypothyroidism.

Thyroxine blood tests are used to determine the levels of T4 hormones in your blood. There are two forms of T4: free T4 and bound T4. Free T4 flows freely through the bloodstream on its own. Bound T4 attaches itself to proteins in the blood. Low amounts of these two types of the T4 hormone indicate an underactive thyroid gland (hypothyroidism), where excessive levels of T4 indicate an overactive thyroid (hyperthyroidism).

Detecting an under or overactive thyroid can help doctors diagnose thyroid-related disorders such as:

- Thyroid cancer

- Goiter: An enlargement of the thyroid gland which can cause pain, hoarseness, swelling, and dizziness.

- Hashimoto’s disease: An autoimmune disorder that attacks cells in the thyroid gland, resulting in hypothyroidism.

- Thyroiditis: Inflammation of the thyroid, which can result in hypothyroidism or hyperthyroidism.

- Grave’s disease: An autoimmune disorder that results in hyperthyroidism.

The thyroid gland produces the hormones triiodothyronine (T3) and thyroxine (T4), which help regulate metabolism. Metabolism can affect your weight, body temperature, and energy. An under or overactive thyroid can alter your heart rhythms, which may lead to heart failure.

Hypothyroidism: An underactive thyroid gland slows down the metabolism, which can lead to weight gain and fatigue. Other symptoms of hypothyroidism include:

  • Sensitivity to cold
  • Constipation
  • Change in menstrual periods
  • Muscle pain/ weakness
  • Joint pain/ stiffness
  • Dry skin and hair
  • Increased cholesterol levels
  • Hoarseness
  • Depression
  • Confusion and memory problems

Hypothyroidism is commonly caused by Hashimoto’s disease, an autoimmune disease in which cells in the thyroid are mistakenly attacked by your body’s immune system. An underactive thyroid can lead to heart problems, mental health problems, nerve damage, infertility, and other complications.

Hyperthyroidism: An overactive thyroid gland produces excessive levels of T3 and T4 hormones. This can produce symptoms such as:

  • Weight loss
  • Rapid heartbeat (tachycardia)
  • Nervousness or anxiety
  • Tremor (trembling in the hands and fingers)
  • Diarrhea
  • Increased appetite
  • Changes in menstrual cycles
  • Sensitivity to heat and excessive sweating
  • Sleep problems
  • Fatigue
  • Bulging eyes (common in Grave’s disease)
  • Hair loss, or thinning of hair

Hyperthyroidism can lead to complications such as heart problems, brittle bones, eye problems (especially common with Grave’s disease), and thyrotoxic crisis. This last condition results in a sudden increase in the severity of your symptoms and delirium. A thyrotoxic crisis is a medical emergency and requires immediate care.

A blood sample is taken to measure T4 levels. To do this, your doctor will insert a small needle into a vein in your forearm. Before the needle is put into your skin, the area will be sanitized. You may feel a pinch as the needle punctures your skin, but this discomfort should subside within a few seconds.

Blood drawn from your arm is deposited in a small vial or tube. Once the desired amount of blood is taken from the arm, the puncture site will be cleaned and bandaged. The vial will be given to the lab for analysis.

T4 tests are quick and do not require sedation. You will be cleared to leave the clinic and resume your daily activities once the testing is finished.

You should receive the results of your T4 test within 1-3 days of your appointment. Your primary care provider will inform you of the results of the analysis. Depending on the findings, you may be asked to come back to the clinic for follow-up testing to definitively diagnose any thyroid conditions. Thyroid cancer may require a biopsy or diagnostic imaging test (such as a CT or X-ray scan).

Hyper/ hypothyroidism treatments are meant to manage hormone levels.

For an underactive thyroid, your doctor may prescribe you a hormone replacement medication that will replace the hormones that your thyroid gland is not producing enough of. The most common medication used for this therapy is levothyroxine, which increases the levels of T4 and T3 in your blood.

For an overactive thyroid, your doctor may prescribe methimazole or propylthiouracil, both of which block your thyroid’s ability to make T4 and T3. You may also be prescribed radioactive iodine, an oral tablet that shrinks your thyroid glands. This leads to a decrease in thyroid hormone production but usually results in permanent damage to the thyroid gland. After taking this medication, you may be prescribed hormone replacement therapy to keep hormone levels balanced.

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