Thyroid Stimulating Immunoglobulin

What is TSI?

The TSI stands for thyroid stimulating immunoglobulin. These are antibodies that have the ability to make the thyroid gland more active resulting in an excess amount of thyroid hormones in the blood.

The thyroid is a gland located the bottom of our neck. Its purpose is to produce many thyroid hormones that can help the body take charge of metabolism, among many others functions. Many health conditions can affect the gland, leading to an over or under production of thyroid hormones.

There are many kinds of thyroid disorders such as hypothyroidism, hyperthyroidism, goiter, thyroid nodules, thyroid cancer and others. Most conditions are accompanied by symptoms like fatigue, weight loss or gain, feeling restless, tremors and palpitations.

Hyperthyroidism is the condition with the most pronounced symptoms. Graves disease is the most common cause of hyperthyroidism. It lets your immune system attack itself by mistake, by producing certain antibodies. As a result, your immune system will produce antibodies that can mimic TSH hormones, leading to more production of hormones. TSI can push the thyroid glands to produce high levels of thyroid hormones, more than needed.

Why take the TSI test?

This test is usually ordered if an individual is showing signs and symptoms of hyperthyroidism, possibly caused by Graves disease. Performing the TSI test can clarify the symptoms and pinpoint the possible causes of an abnormal thyroid panel. For pregnant women, TSI are capable to crossover from the blood of the mom to the placenta. These would be able to interact with the thyroid gland of the baby, causing a condition called “neonatal graves thyrotoxicosis”. The TSI test is typically ordered during the last three months of pregnancy.

What your TSI test results mean?

Normal values of a TSI test are less than a hundred and thirty percent of base of activity. Different laboratories use different measurements; so, normal value ranges may differ slightly. When your levels are higher than normal, this may indicate that you have graves disease (which is the most common), hashitoxicosis (that is very rare), or neonatal thyrotoxicosis. In the case of the neonatal thyrotoxicosis, if the baby is treated properly, thyroid functions will not be affected. Thyrotoxicosis refers to hyperthyroidism.

Abnormal levels of TSI maybe do you two conditions like Hashimoto thyroiditis, chronic lymphocytic thyroiditis, and toxic goiter. Hashimoto usually causes a decrease in the function of the thyroid gland. In toxic goiter, the thyroid gland is enlarged and has many nodules. As a result, too much thyroid hormones will be produced.

Sometimes, it is possible that a single result could be normal, but the individual may still have an autoimmune disorder. In that case, the test may need to be repeated at a later time.

Where can I get a TSI test near me?

Please use our Lab Locator to find find a convenient testing location.

Reviewed By: Dr. Kurt Kloss, MD
Last Reviewed Date: Feb 28, 2020