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Thyroid Blood Tests (cont.)

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How is hypothyroidism diagnosed?

A diagnosis of hypothyroidism can be suspected in patients with fatigue, cold intolerance, constipation, and dry, flaky skin. A blood test is needed to confirm the diagnosis.

When hypothyroidism is present, the blood levels of thyroid hormones can be measured directly and are usually decreased. However, in early hypothyroidism, the level of thyroid hormones (T3 and T4) may be normal. Therefore, the main tool for the detection of hyperthyroidism is the measurement of the TSH, the thyroid stimulating hormone. As mentioned earlier, TSH is secreted by the pituitary gland. If a decrease of thyroid hormone occurs, the pituitary gland reacts by producing more TSH and the blood TSH level increases in an attempt to encourage thyroid hormone production. This increase in TSH can actually precede the fall in thyroid hormones by months or years (see the section on Subclinical Hypothyroidism below). Thus, the measurement of TSH should be elevated in cases of hypothyroidism. However, there is one exception. If the decrease in thyroid hormone is actually due to a defect of the pituitary or hypothalamus, then the levels of TSH are abnormally low. As noted above, this kind of thyroid disease is known as "secondary" or "tertiary" hypothyroidism. A special test, known as the TRH test, can help distinguish if the disease is caused by a defect in the pituitary or the hypothalamus. This test requires an injection of the TRH hormone and is performed by an endocrinologist (hormone specialist).

Are there other tests of the thyroid gland?

The blood tests mentioned above can confirm the presence of deficiency or an excess of thyroid hormone and, therefore, be 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 others.

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.

Medically reviewed by John A. Seibel, MD; Board Certified Internal Medicine with a subspecialty in Endocrinology & Metabolism

REFERENCE:

National Endocrine and Metabolic Diseases Information Service (NEMDIS)
http://endocrine.niddk.nih.gov/pubs/thyroidtests/index.aspx


Medically Reviewed by a Doctor on 1/24/2014

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Thyroid Blood Tests – Hypothyroidism Diagnosis Question: What were the results of your thyroid blood tests?
Thyroid Blood Tests - Why Testing Question: Why did you have thyroid blood tests performed?
Source: MedicineNet.com
http://www.medicinenet.com/thyroid_blood_tests/article.htm

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