What is a TSI test?
The TSI test measures the level of thyroid-stimulating
immunoglobulin (TSI) in your blood. High levels of TSI in the blood can indicate
the presence of Graves’ disease, which is an autoimmune disorder that affects
the thyroid gland.
If you have Graves’ disease, you’re more likely to develop
other autoimmune diseases such as type 1 diabetes or Addison’s disease. Women
to 8 times more likely to develop Graves’ disease than men. Rarely, the TSI
test can be used to diagnose other disorders that affect the thyroid, such as Hashimoto’s
thyroiditis and toxic multinodular goiter.
Your doctor may order a TSI test if you have signs of
hyperthyroidism or if you’re pregnant and have a history of thyroid problems.
How does TSI affect your thyroid?
The thyroid is an endocrine gland. It’s located at the base
of your neck. Your thyroid is responsible for the production of various thyroid
hormones that help your body regulate metabolism and other important functions.
Several conditions can cause your thyroid to produce too much
of the thyroid hormones T3 and T4. When this occurs, it’s known as
hyperthyroidism. Hyperthyroidism can lead to a range of symptoms, including:
- weight loss
When hyperthyroidism suddenly worsens, it’s known as thyroid
storm, which is a life-threatening condition. This occurs when there is a surge
of thyroid hormone in the body. Usually, it occurs due to untreated or
undertreated hyperthyroidism. This is a medical emergency that requires
“Thyrotoxicosis” is an older term for hyperthyroidism due to
Graves’ disease is one of the most common causes of
hyperthyroidism. If you have Graves’ disease, your immune system mistakenly
produces the antibody TSI. TSI mimics thyroid-stimulating hormone (TSH), which
is the hormone that signals your thyroid to produce more T3 and T4.
TSI can trigger your thyroid to produce more thyroid hormones
than necessary. The presence of TSI antibodies in your blood is an indicator
that you may have Graves’ disease.
What is the purpose of a TSI test?
Diagnosis of Graves’ disease
Your doctor will typically order a TSI test if you are
showing signs of hyperthyroidism and they suspect that you might have Graves’
disease. Graves’ disease is the most common cause of hyperthyroidism. This test
can help clarify the cause of your symptoms when your TSH, T3, and T4 levels
In pregnant women
Your doctor may also perform this test during pregnancy if
you have symptoms of hyperthyroidism or a history of thyroid problems. Graves’
hyperthyroidism affects about 2 out of 1000 pregnancies.
If you have Graves’ disease, the TSI in your bloodstream can
cross the placenta. Those antibodies can interact with your baby’s thyroid and result
in a condition called “transient neonatal Graves’ thyrotoxicosis.” This means
that although your baby will be born with Graves’ disease, it’s treatable,
temporary, and will pass after the excess TSI leaves your baby’s body.
Diagnosis of other diseases
Other disorders related to abnormal TSI levels include Hashimoto’s
thyroiditis and toxic multinodular goiter. Also called chronic lymphocytic thyroiditis,
Hashimoto’s thyroiditis is inflammation and swelling of the thyroid gland. It typically
decreases the function of the thyroid gland, causing hypothyroidism. In toxic
multinodular goiter, your thyroid gland is enlarged and has a number of small,
round growths, or nodules, that produce too much thyroid hormone.
Preparation and procedure
This test doesn’t generally require any preparation, such as
fasting or stopping medications. However, if your doctor asks you to do so,
follow their instructions. They may want to draw blood for other tests that
require fasting at the same time as your TSI test.
When you arrive for the procedure, a healthcare provider
will take a sample of your blood. They’ll send your blood sample to a
laboratory, where it will be tested to determine your TSI level.
What do your TSI test results mean?
TSI test results are in the form of a percentage or TSI index.
Usually, a TSI index of less than 1.3, or 130 percent,
is considered normal.
Your doctor might have different standards, so you should ask your doctor if
you have any questions or concerns.
It’s possible for you to have an autoimmune disorder despite
having a normal TSI test result. If your doctor suspects that the antibodies
might develop over time, as is the case with some autoimmune disorders, then
repeat testing at a later date may be necessary.
If you have elevated TSI levels, it might indicate that you
- Graves’ disease
- hashitoxicosis, which is increased thyroid
activity due to inflammation related to Hashimoto’s thyroiditis
- neonatal thyrotoxicosis, in which your baby has
high levels of thyroid hormones at birth because of your high levels of thyroid
With treatment, neonatal thyrotoxicosis in your baby will
If TSI is present in the blood, it’s often an indication of
Risks of the TSI test
Every blood test has some risks, which include the
- minor pain during and shortly after the
- slight bleeding after the healthcare provider
removes the needle
- the development of a small bruise in the area of
the puncture site
- an infection in the area of the puncture site,
which is rare
- inflammation of the vein in the area of the
puncture site, which is rare