- Thyroid Hormones
- Normal Levels
- Types of Thyroid Disorders
What are thyroid hormones?
The thyroid gland produces hormones that are essential for normal body metabolism. Blood testing is now commonly available to determine the adequacy of the levels of thyroid hormones. These blood tests can define whether the thyroid gland's hormone production is normal, overactive, or underactive.
The thyroid gland is located in the lower part of the neck, below the Adam's apple.The gland wraps around the windpipe (trachea) and has a shape that is similar to a butterfly - formed by two wings (lobes) and attached by a middle part (isthmus).
- The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), which account for 99.9% and 0.1% of thyroid hormones present in the blood respectively.
- However, the hormone with the most biological activity is T3.
- Once released from the thyroid gland into the blood, a large amount of T4 is converted into T3 - the active hormone that affects the metabolism of cells.
What are normal thyroid hormone levels?
The thyroid itself is regulated by another gland that is located in the brain, called the pituitary. In turn, the pituitary is regulated in part by the thyroid (via a "feedback" effect of thyroid hormone on the pituitary gland) and by another gland called the hypothalamus.
The hypothalamus releases a hormone called thyrotropin releasing hormone (TRH), which sends a signal to the pituitary to release thyroid stimulating hormone (TSH). In turn, TSH sends a signal to the thyroid to release thyroid hormones. If a disruption occurs at any of these levels, a defect in thyroid hormone production may result in a deficiency of thyroid hormone (hypothyroidism).
Hypothalamus - TRH
Pituitary - TSH
Thyroid - T4 and T3
The rate of thyroid hormone production is controlled by the pituitary gland. If there is an insufficient amount of thyroid hormone circulating in the body to allow for normal functioning, the release of TSH is increased by the pituitary gland in an attempt to stimulate more thyroid hormone production. In contrast, when there is an excessive amount of circulating thyroid hormone, TSH levels fall as the pituitary attempts to decrease the production of thyroid hormone.
- In persons with hypothyroidism (thyroid hormone production is below normal), there is a continuously decreased level of circulating thyroid hormones.
- In persons with hyperthyroidism (thyroid hormone production is above normal), there is a continuously elevated level of circulating thyroid hormones.
What are the types of thyroid disorders?
The most common thyroid disorders include:
What procedures and tests diagnose thyroid problems?
Blood tests are used to diagnose hypothyroidism or hyperthyroidism. They do not point to a specific cause. In order to determine a cause of the thyroid abnormality, the doctor will consider the patient's history, physical examination, and medical condition. Further testing might be used to isolate an underlying cause. These tests might include more blood testing for
- thyroid antibodies,
- nuclear medicine thyroid scanning,
- ultrasound of the thyroid gland, or
If thyroid cancer is suspected and surgery may be required, your physician may ask for a blood test known as thyroglobulin.
- Thyroglobulin is a protein made only by thyroid cells.
- If the thyroglobulin level at baseline is detectable or elevated (this means the gland does in fact make the protein) it can be used as a tumor marker.
- After a total thyroidectomy for cancer (removal of the entire thyroid gland) the level should fall to an undetectable range since the cells that make thyroglobulin have been removed.
- If the level remains detectable after surgery, there is a possibility of thyroid tissue elsewhere in the body, and metastatic disease should be considered.
- If the level is undetectable for a period of time after surgery and then starts to climb, a recurrence of the cancer - either at the primary site or elsewhere in the body should be considered.
Latest Thyroid News
Daily Health News
Health Solutions From Our Sponsors
National Endocrine and Metabolic Diseases Information Service (NEMDIS).
Top Thyroid Blood Tests Related Articles
DizzinessDizziness is a symptom that often applies to a variety of sensations including lightheadedness and vertigo. Causes of dizziness include low blood pressure, heart problems, anemia, dehydration, and other medical conditions. Treatment of dizziness depends on the cause.
Fine-Needle Aspiration Biopsy of the ThyroidFine needle aspiration biopsy of the thyroid is used to obtain tissue for analysis. Fine needle aspiration is also performed to treat thyroid cysts. The fine needle aspiration biopsy procedure may be recommended to make the diagnosis and/or select therapy of a thyroid nodule. Fine needle aspiration biopsy may also be recommended to drain or shrink a thyroid cyst.
25 Hormone Imbalance Symptoms and SignsHormone imbalance including abnormal levels of estrogen, testosterone, cortisol, progesterone, and other hormones may lead to symptoms like weight gain, fatigue, and mood swings. Hormonal imbalance may be due to natural states, like menopause, or other conditions. See your doctor for suspected imbalances in hormonal systems.
Hyperthyroidism is an excess of thyroid hormone due to an overactive thyroid gland. Symptoms can include increased heart rate, weight loss, heart palpitations, frequent bowel movements, depression, fatigue, fine or brittle hair, sleep problems, thinning skin, and irregular vaginal bleeding.
Graves' disease is the most common cause of hyperthyroidism. Many other health problems or taking excess thyroid hormone medication can cause an overactive thyroid gland. Treatment for the condition is with medication, radioactive iodine, thyroid surgery (rarely), or reducing the dose of thyroid hormone. No diet has been shown to treat hyperthyroidism or its symptoms and signs.
Hyperthyroidism SlidesWhat is hyperthyroidism? Hyperthyroidism occurs when an overactive thyroid gland produces an excessive amount of thyroid hormones. Learn hyperthyroidism causes, symptoms, and treatment.
Hypothyroidism is any state in which thyroid hormone production is below normal. Normally, the rate of thyroid hormone production is controlled by the brain by the pituitary gland. Hypothyroidism is a very common condition and the symptoms of hypothyroidism are often subtle, but may include, constipation, memory loss, hair loss, and depression. There are a variety of causes of hypothyroidism, and treatment depends on the cause.
Hypothyroidism During Pregnancy
Hypothyroidism during pregnancy can be treated with synthetic thyroid hormones to maintain the proper thyroid hormone balance. Hypothyroidism symptoms include fatigue, weight gain, lethargy, and constipation. Treatment of hypothyroidism in pregnant women is important, because inadequate levels of thyroid hormones may affect the fetus, and child during growth and development.
Thyroid Disorders Symptoms and SignsThyroid diseases and disorders are caused because the body either makes too much or too little thyroid hormones, which are necessary for vital functions of the body.
Thyroid disease and disorder symptoms and signs depend on the type of the thyroid problem. Examples include heat or cold intolerance, sweating, weight loss or gain, palpitations, fatigue, dry skin, constipation, brittle hair, joint aches and pains, heart palpitations, edema, feeling bloated, puffiness in the face, reduced menstrual flow, changes in the frequency of bowel movements and habits, high cholesterol, hoarseness, brittle hair, difficulty swallowing, shortness of breath, a visible lump or swelling in the neck, tremors, memory problems, depression, nervousness, agitation, irritability, or poor concentration.
Thyroid problems are more common in women.
Thyroid DisordersThere are several types of thyroid disorders including hypothyroidism, hyperthyroidism, goiters, thyroid nodules, and thyroid cancer. Symptoms vary by condition. Diagnosis is made with blood tests, scans, ultrasound, or biopsy. Treatments depend on the disorder and can include medication or surgery.
Thyroid NodulesThyroid nodules are the most common endocrine problem in the United States. The term thyroid nodule refers to any abnormal growth that forms a lump in the thyroid gland. The vast majority of thyroid nodules are benign.
Thyroid Peroxidase TestThe thyroid peroxidase test measures the level of an antibody that is directed against thyroid peroxidase (TPO). A presence of TPOAb in the blood reflects a prior attack by the body's immune system on thyroid tissue. A positive thyroid peroxidase test may signal chronic thyroiditis. Other autoimmune disorders, however, may have a positive TPOAb test.
Illustrations of ThyroidThe thyroid is a butterfly-shaped gland located in the front of the neck just below the Adams apple. See a picture of the Thyroid and learn more about the health topic.
Thyroid SlideshowLearn about thyroid problems such as hyperthyroidism, hypothyroidism, thyroid cancer, and more. Discover symptoms and treatments for various thyroid problems.
Thyroid QuizYour unexplained change in weight could indicate a thyroid condition. Take the Thyroid Quiz to learn about common symptoms and treatments of overactive and underactive thyroid disorders.
Thyroid ScanThyroid scanning is used to determine how active the thyroid is in manufacturing thyroid hormone. This can determine whether inflammation of the thyroid gland (thyroiditis) is present. It can also detect the presence and degree of overactivity of the gland (hyperthyroidism) or, conversely, it can determine the presence and degree of underactivity of the gland (hypothyroidism).