A thyroid-stimulating immunoglobulin (TSI) test is a blood test that can help diagnose Graves’ disease, an autoimmune condition that causes an overactive thyroid.

A TSI test measures levels of TSIs in the blood. TSIs are antibodies that can overstimulate the thyroid gland. A positive TSI test result allows doctors to recommend treatments for Graves’ disease.

This article provides an overview of a TSI-level test, including the procedure, risks, results, and next steps.

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According to a 2023 overview of research, healthcare professionals use TSI tests to diagnose Graves’ disease. This condition is the most common cause of hyperthyroidism, where the thyroid gland becomes overactive and produces excessive thyroid hormones.

In people with Graves’ disease, TSI levels can be above average. This is because TSI is a thyroid antibody that can stimulate the thyroid.

Thyroid antibodies are cells that attack the thyroid. The body produces them when it mistakes thyroid cells for invading pathogens.

There is also evidence that TSI tests can help determine the outlook for people with Graves’ disease. However, more research is necessary to confirm this.

The TSI test involves a blood test. Some blood tests require someone to avoid eating or drinking for up to 12 hours before the test and to stop taking certain medications.

According to Lab Tests Online-UK, a person does not need to take any steps to prepare for a TSI blood test. However, individuals need to speak with a doctor to ensure that they do not need to take preparatory measures.

Before taking the sample, the healthcare professional will place a tourniquet around the upper arm. A tourniquet is a tight band that temporarily restricts blood flow. This causes the veins to swell, making it easier to take the blood sample.

A healthcare professional will usually extract a blood sample from a blood vessel in the person’s arm. The healthcare professional will typically aim to withdraw blood from around the inner elbow or wrist, where the veins are closer to the surface of the arm.

A doctor or nurse will clean the skin with an antiseptic wipe. They will insert a needle and draw the blood. This may cause a prickling or scratching sensation, which should not be very painful.

The medical professionals can then remove the tourniquet and the needle and apply pressure to the area using cotton wool.

There is some scientific debate about how to interpret TSI test results. However, a 2022 study proposes that anything above 0.577 international units of TSI per liter of blood indicates Graves’ disease.

The study authors argue that this is the most useful cutoff value for diagnostic purposes.

A TSI test can differentiate between Graves’ disease and other forms of hyperthyroidism. However, further tests may be necessary to determine the extent of hyperthyroidism in Graves’ disease.

Once doctors have all the information they need, they can proceed to treatment, which involves reducing the production of thyroid hormones.

Treatment for Graves’ disease includes:

  • Medications: A doctor may prescribe beta-blockers to reduce a person’s symptoms. Antithyroid medications can include methimazole and propylthiouracil. Although methimazole is the common antithyroid medication, a doctor may prescribe propylthiouracil for those in the first 3 months of pregnancy to reduce the risk of harm to the fetus.
  • Radioiodine therapy: This involves taking radioactive iodine in the form of a pill or liquid.
  • Thyroidectomy: A person may need surgery to remove part of the thyroid.

According to the NHS (National Health Service), blood tests come with a few small risks.

These include pain and bruising. Some people may also feel faint or dizzy just after the test. If this occurs, they can discuss it with the health professional who administered the test.

Doctors perform TSI-level tests to diagnose Graves’ disease, which is the most common cause of hyperthyroidism. It arises when there are high levels of TSI — an antibody that overstimulates the thyroid gland.

The TSI test is a blood test, which involves drawing a sample of blood, usually from a vein in the arm. Doctors can then send the sample of blood to a laboratory for testing. If an individual has over 0.577 international units of TSI per liter of blood, they may have Graves’ disease.