TSH Blood Test and Other Thyroid Blood Tests

A thyroid blood test (TSH blood test and T4 blood test) is performed to assess how well the thyroid gland is functioning. These test are also used to diagnose and help find the cause of thyroid disorders such as hyperthyroidism and hypothyroidism.

What blood tests does Cardio-Med use to assess a person's thyroid function?

The thyroid blood tests done at Cardio-Med includes the following:

Based on the results of the TSH test and T4 test and other considerations, additional thyroid blood tests are sometimes needed. Examples are:

Your Cardio-Med physician takes a patient's full medical history into account when interpreting thyroid function tests.

TSH Test
The TSH test is done to check how well the thyroid gland is working. It measures the amount of TSH a person's pituitary gland is secreting. The TSH test is the most accurate test for diagnosing both hyperthyroidism and hypothyroidism. Generally, a below-normal level of TSH suggests hyperthyroidism (an overactive thyroid). An abnormally high TSH level suggests hypothyroidism (an underactive thyroid).

The TSH test detects even tiny amounts of TSH in the blood. Normally, the pituitary boosts TSH production when thyroid hormone levels in the blood are low. The thyroid responds by making more hormone. Then, when the body has enough thyroid hormone circulating in the blood, TSH output drops. The cycle repeats continuously to maintain a healthy level of thyroid hormone in the body. In people whose thyroid produces too much thyroid hormone, the pituitary shuts down TSH production, leading to low or even undetectable TSH levels in the blood.

In people whose thyroid gland produces too little thyroid hormone, the pituitary keeps making TSH, trying to get the thyroid gland to increase production. This results in a higher level of circulating TSH.

If results of the TSH test are abnormal, one or more additional tests are needed to find the cause of the problem.

T4 Tests
The thyroid primarily secretes T4 and only a small amount of T3. T4 exists in two forms:
  1. T4 that is bound to proteins in the blood and is kept in reserve until needed
  2. a small amount of unbound or "free" T4 (FT4), which is the active form of the hormone and is available to enter body tissues when needed

A high level of total T4 (bound and FT4) or FT4 alone suggests hyperthyroidism, and a low level of total T4 or FT4 suggests hypothyroidism.

Both pregnancy and taking oral contraceptives increase levels of binding protein in the blood. In either of these cases, although a woman may have a high total T4 level, she may not have hyperthyroidism. Severe illness or the use of corticosteroids-a class of medications that treat asthma, arthritis, and skin conditions, among other health problems-can decrease binding protein levels. Therefore, in these cases, the total T4 level may be low, yet the person does not have hypothyroidism.

T3 Test
If hyperthyroidism is suspected in a person who has a normal FT4 level, a T3 test can be useful to confirm the condition. In some cases of hyperthyroidism, FT4 is normal yet free T3 (FT3) is elevated, so measuring both T4 and T3 can be useful if your physician suspects hyperthyroidism. The T3 test is not useful in diagnosing hypothyroidism because levels are not reduced until the hypothyroidism is severe.
TSI Test
Thyroid-stimulating immunoglobulin is an autoantibody present in Graves' disease. TSI mimics TSH by stimulating the thyroid cells, causing the thyroid to secrete extra hormone. The TSI test detects TSI circulating in the blood and is usually measured
Antithyroid Antibody Test
The antithyroid antibody test detects certain autoantibodies present in autoimmune thyroid disease. Autoantibodies are molecules produced by a person's body that mistakenly attack the body's own tissues. Two principal types of antithyroid antibodies are
  1. anti-TG antibodies, which attack a protein in the thyroid called thyroglobulin
  2. anti-thyroperoxidase, or anti-TPO, antibodies, which attack an enzyme in thyroid cells called thyroperoxidase

Hashimoto's disease is an example of thyroid autoimmune disease in which thyroid autoantibodies are produced.

What imaging tests does Cardio-Med use to diagnose and find the cause of thyroid disorders?

Your physician may take an ultrasound scan of the thyroid or perform nuclear medicine tests to diagnose and find the cause of thyroid disorders.

Ultrasound. Ultrasound uses a device, called a transducer, that bounces safe, painless sound waves off organs to create an image of their structure. A specially trained technician performs the procedure in our office, and a radiologist-a physician who specializes in medical imaging-interprets the images; a patient does not need anesthesia. The images can show the size and texture of the thyroid, as well as a pattern of typical autoimmune inflammation. The images can also show nodules or growths within the gland that suggest a malignant tumor.

Nuclear medicine tests. Nuclear medicine tests of the thyroid include a thyroid scan and a radioactive iodine uptake test. People often have to follow a low iodine diet prior to having the tests. Read more about a low iodine diet from the American Thyroid Association at www.thyroid.org/faq-low-iodine-dietExternal Link Disclaimer.

We also offer a body scan that provides ultrasound imaging of body organs and a test for stroke to check carotid artery blood flow to the brain. This suite of tests including the complete physical exam gives your physician a complete view of your state of health.

Call (847)758-1230 today for an appointment and consultation with our physician.
Serving Chicago, IL and all of the Chicago northwest suburbs, southeastern Wisconsin and northwestern Indiana.

Adapted from the American Thyroid Association

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