Thyroid Stimulating Immunoglobulin (TSI) Test

The Thyroid Stimulating Immunoglobulin, or TSI, test measures the level of thyroid stimulating antibodies in your blood. TSI is a type of immunoglobulin G antibody that can bind to thyroid stimulating hormone receptors on the thyroid gland. When these antibodies attach to the receptors, they mimic the action of TSH and stimulate the thyroid to produce excessive amounts of thyroid hormones.

Unlike normal TSH regulation, TSI antibodies are not controlled by the body’s feedback system. This can lead to persistent overproduction of thyroxine, T4, and triiodothyronine, T3, resulting in hyperthyroidism. Measuring TSI levels helps determine whether an autoimmune process is driving abnormal thyroid hormone production.

The TSI test is most commonly used to help diagnose Graves disease, an autoimmune disorder and one of the leading causes of hyperthyroidism. In Graves disease, elevated TSI antibodies overstimulate the thyroid gland, causing symptoms such as weight loss, rapid heartbeat, heat intolerance, and an enlarged thyroid.

Although high TSI levels are most strongly associated with Graves disease, they may also be present in other autoimmune thyroid conditions, including certain cases of Hashimoto thyroiditis. Identifying elevated TSI provides critical insight into the underlying cause of thyroid imbalance and helps guide targeted treatment decisions.

What Is Included In This Test?

This test includes:

• Measurement of Thyroid Stimulating Immunoglobulin levels in the blood
• Laboratory analysis to detect autoimmune stimulation of the thyroid
• Clear numerical results for clinical interpretation

This test focuses specifically on TSI antibodies and does not include TSH, T3, or T4 unless ordered separately.

Why Does This Test Matter?

Hyperthyroidism can significantly impact heart function, metabolism, mood, and overall health. Identifying whether an autoimmune condition is the cause is essential for accurate diagnosis and appropriate treatment.

High TSI levels strongly suggest Graves disease, which is a treatable autoimmune disorder. Early detection allows for proper management, symptom control, and prevention of complications such as heart rhythm abnormalities or bone loss.

The TSI test is also useful in distinguishing Graves disease from other causes of hyperthyroidism. This distinction is important because treatment approaches may differ depending on the underlying cause.

For individuals with a history of Graves disease, monitoring TSI levels may help assess disease activity or predict relapse.

Who Should Consider This Test?

You may consider this test if you:

• Have symptoms of hyperthyroidism such as weight loss or rapid heartbeat
• Experience heat intolerance or excessive sweating
• Have an enlarged thyroid gland
• Have abnormal TSH, T3, or T4 results
• Are being evaluated for Graves disease
• Have bulging eyes or other signs of thyroid eye disease
• Have a family history of autoimmune thyroid disease
• Are pregnant with a history of Graves disease
• Are monitoring treatment for autoimmune hyperthyroidism
• Want to determine if hyperthyroidism is autoimmune-related

Convenient, No-Appointment Testing

To complete your test:

1. Order online through our website
2. Use the lab locator to find a nearby testing location
3. Walk in; no appointment required
4. Access your results securely in your HealthLabs.com account within one to three business days

110% Price Guarantee!

If you find the same test for a lower price from a comparable provider, contact us. We not only match the price, we beat it by an additional 10 percent of the difference.