Test library
Thyroid Stimulating Immunoglobulin Test
TSI testing measures thyroid stimulating immunoglobulin, an autoantibody that mimics TSH and overstimulates the thyroid. It is used to help evaluate Graves disease and other forms of hyperthyroidism.
Order TSI Test - Thyroid Stimulating Blood Test
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Order TSI Test - Thyroid Stimulating Blood Test- Typical turnaround
- 1-3 business days
- Starting price
- From $119
- Results
- Confidential, online
Quick answer
TSI testing measures thyroid stimulating immunoglobulin in a blood sample. This autoantibody binds to the TSH receptor and can stimulate the thyroid gland to produce excess hormone, which is why it is closely associated with Graves disease. The test is typically ordered when hyperthyroidism is suspected or when a provider wants to confirm an autoimmune cause. Results are interpreted alongside TSH, free T4, and free T3.
What this test measures
Thyroid stimulating immunoglobulin is an autoantibody that targets the TSH receptor on thyroid cells. Instead of merely blocking the receptor, it activates it, prompting the gland to release more thyroid hormone. This activity distinguishes it from other thyroid antibodies and links it directly to the overactive thyroid seen in Graves disease. Measuring TSI gives a functional view of what the immune system is doing.
The test requires a blood sample drawn from a vein, usually at the arm, and no special preparation is typically needed. Laboratories use assays such as the thyrotropin receptor antibody or TSI bioassay to detect and often quantify the antibody. The reported value reflects the level of stimulating activity and is compared against a reference range established by the performing laboratory.
TSI testing is commonly ordered when a person has signs of hyperthyroidism, such as a rapid heartbeat, weight loss, heat intolerance, or an enlarged thyroid. It can help distinguish Graves disease from other causes of an overactive thyroid, including toxic nodules or thyroiditis. Providers may also use it to monitor disease activity or assess thyroid antibody status during pregnancy planning.
Results are not a stand-alone diagnosis. Antibody levels can fluctuate, and some people with Graves disease have low or undetectable TSI, while others without active disease may show low levels. A qualified healthcare provider interprets the result together with thyroid function tests, symptoms, and imaging to reach an accurate assessment.
- Thyroid stimulating immunoglobulin (TSI)
- TSH receptor antibodies (TRAb)
- TSH (thyroid stimulating hormone)
- Free T4 (thyroxine)
- Free T3 (triiodothyronine)
- Total T4
- Total T3
- Thyroid peroxidase (TPO) antibodies
- Thyroglobulin antibodies
Why people order this test
- Investigate suspected hyperthyroidism or an overactive thyroid
- Help confirm an autoimmune cause such as Graves disease
- Support monitoring of Graves disease activity over time
- Distinguish Graves disease from other causes of hyperthyroidism
- Assess thyroid antibody status during pregnancy planning
- Follow up on abnormal thyroid function tests
How to prepare
No fasting is usually required for TSI testing, and a blood sample can be collected at any time of day unless the laboratory specifies otherwise. Tell the ordering provider about any medications or supplements you take, since some can affect thyroid results.
Understanding your results
Results are generally reported within one to three business days. An elevated TSI can support a diagnosis of Graves disease, while a normal result does not rule out thyroid autoimmunity. A qualified healthcare provider interprets the value with the rest of your thyroid panel.
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Frequently Asked Questions
What does the TSI test measure?
It measures thyroid stimulating immunoglobulin, an autoantibody that activates the TSH receptor and can drive the thyroid to produce excess hormone.
Why is TSI testing ordered?
It is usually ordered to help confirm Graves disease or another autoimmune cause when hyperthyroidism is suspected, and sometimes to monitor disease activity.
How is TSI different from other thyroid antibody tests?
Antibodies such as TPO or thyroglobulin antibodies mark autoimmune thyroid disease in general. TSI specifically reflects stimulating activity at the TSH receptor.
Do I need to fast before a TSI test?
Fasting is not normally required. Follow any instructions the laboratory provides, especially if the test is bundled with other panels.
Can TSI be normal in Graves disease?
Yes. Antibody levels can vary between people and over time, so a normal result does not completely exclude the condition. Providers consider the full clinical picture.
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