TSI (Thyroid Stimulating Immunoglobulin) Biomarker Testing
A TSI test checks thyroid-stimulating antibodies linked to Graves’ disease, with convenient ordering and Quest-based lab collection through Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
TSI (thyroid stimulating immunoglobulin) is an antibody test that helps explain why your thyroid may be “stuck on.” When TSI is present at higher levels, it can stimulate your thyroid gland to produce too much thyroid hormone, which is a common pattern in Graves’ disease.
If you have symptoms of hyperthyroidism—such as palpitations, heat intolerance, tremor, anxiety, unintentional weight loss, or frequent bowel movements—TSI can help clarify whether an autoimmune process is driving those symptoms.
TSI is most useful when it is interpreted alongside thyroid function tests (TSH, free T4, and sometimes free T3) and your clinical picture. One number rarely tells the whole story, but this test can be a key piece of the puzzle.
Do I need a TSI Thyroid Stimulating Immunoglobulin test?
You may benefit from a TSI test if your thyroid labs or symptoms suggest hyperthyroidism and you want to understand the likely cause. TSI is especially relevant when your TSH is low and your free T4 and/or free T3 are high, because it can support an autoimmune explanation rather than a temporary thyroiditis pattern.
This test is also commonly used when you have signs that point toward Graves’ disease, such as a diffuse goiter (enlarged thyroid), new eye symptoms (grittiness, pressure, bulging, or double vision), or a history of autoimmune disease in you or your family.
If you are already being treated for Graves’ disease, TSI can sometimes help with monitoring and planning. For example, your clinician may use trends in antibody activity—along with your thyroid hormone levels—to help guide decisions about medication adjustments, remission assessment, or relapse risk.
TSI testing supports clinician-directed care and follow-up; it is not, by itself, a standalone diagnosis.
TSI is measured using a CLIA-certified laboratory immunoassay; results should be interpreted with your symptoms, exam findings, and thyroid function tests rather than used as a self-diagnosis.
Lab testing
Order a TSI test and get clear next-step guidance when your results arrive.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
Vitals Vault makes it straightforward to order a TSI test when you are trying to confirm whether hyperthyroid symptoms or abnormal thyroid labs may be autoimmune in origin. You can order online and complete your blood draw through a Quest-based lab collection network.
Once your results are in, PocketMD can help you make sense of what “positive,” “negative,” or “borderline” means in plain language and how your TSI result fits with TSH, free T4, free T3, and other thyroid antibodies. You can also use PocketMD to prepare questions for your next appointment, especially if you are deciding on next steps such as imaging, medication changes, or retesting.
If your situation calls for broader thyroid mapping, you can add companion thyroid tests so you are not interpreting TSI in isolation.
- Order online and test through a Quest-based lab collection network
- PocketMD guidance to help you interpret results and plan next steps
- Easy retesting to track trends over time when clinically appropriate
Key benefits of TSI Thyroid Stimulating Immunoglobulin testing
- Helps identify Graves’ disease as a cause of hyperthyroidism when thyroid hormones are high and TSH is low.
- Distinguishes autoimmune stimulation from other causes of thyrotoxicosis, such as thyroiditis or excess thyroid hormone intake.
- Supports decision-making when symptoms suggest hyperthyroidism but the picture is not yet clear.
- Provides useful context when you have thyroid eye symptoms and Graves’ disease is being considered.
- Can be followed over time in some treatment plans to help assess remission or relapse risk alongside thyroid function tests.
- Improves interpretation of thyroid labs when combined with TSH, free T4, free T3, and other thyroid antibodies.
- Gives you a concrete data point to discuss with your clinician, with PocketMD support for next-step planning.
What is TSI Thyroid Stimulating Immunoglobulin?
TSI stands for thyroid stimulating immunoglobulin. It is an autoantibody, meaning your immune system makes it and it targets your own tissue. In this case, the antibody binds to the thyroid-stimulating hormone (TSH) receptor on thyroid cells.
When TSI activates the TSH receptor, it can “mimic” TSH and tell the thyroid gland to produce and release more thyroid hormone than your body needs. That overproduction can lead to hyperthyroidism (thyrotoxicosis), with symptoms such as rapid heartbeat, tremor, anxiety, heat intolerance, and weight loss.
TSI is closely associated with Graves’ disease, the most common cause of persistent hyperthyroidism in many adults. Not every lab uses the same antibody method or reporting units, and some reports use related terms like TRAb (TSH receptor antibodies). Your clinician may choose one test or the other depending on the clinical question and the lab method available.
TSI vs TRAb: what’s the difference?
TRAb is a broader category that includes antibodies that bind the TSH receptor. Some TRAb antibodies stimulate the receptor (like TSI), while others can block it. A TSI assay is designed to detect stimulating activity more specifically, which can be helpful when the goal is to support a Graves’ pattern.
How TSI fits with TSH, free T4, and free T3
TSI helps explain the “why,” while TSH and thyroid hormones show the “what.” In Graves’ disease, you often see low TSH with elevated free T4 and/or free T3. A positive or elevated TSI supports an autoimmune driver for that hormone pattern.
Why symptoms alone are not enough
Many hyperthyroid symptoms overlap with anxiety, stimulant use, perimenopause, infection, and other medical issues. TSI does not replace a full evaluation, but it can reduce uncertainty when your symptoms and thyroid labs point toward an autoimmune cause.
What do my TSI Thyroid Stimulating Immunoglobulin results mean?
Low or negative TSI
A low or negative TSI result means the test did not detect significant thyroid-stimulating antibody activity. If your thyroid hormones are normal, that often makes Graves’ disease less likely at that moment. If you are clearly hyperthyroid, a negative TSI does not completely rule out Graves’ disease, because antibody levels can vary by assay, timing, and individual biology. Your clinician may consider repeat testing, TRAb testing, or other evaluation such as thyroid uptake imaging depending on your case.
In-range TSI (within the lab’s reference interval)
An in-range result generally suggests there is no strong evidence of thyroid-stimulating antibodies driving your thyroid function right now. If you have symptoms but normal thyroid function tests, this can be reassuring and may shift attention to other causes of your symptoms. If you are being treated for Graves’ disease, an in-range or falling TSI trend can be one supportive sign of improving autoimmune activity, but treatment decisions still rely heavily on TSH and thyroid hormone levels.
High or positive TSI
A high or positive TSI result supports an autoimmune process that can stimulate the thyroid gland, which is commonly seen in Graves’ disease. When this result occurs alongside low TSH and elevated free T4 and/or free T3, it strengthens the case that Graves’ is the cause of hyperthyroidism. Higher antibody activity can also correlate with a higher likelihood of persistent disease in some people, although the relationship is not perfect. Your next steps usually include confirming the full thyroid lab pattern, reviewing medications and supplements, and discussing treatment and monitoring with your clinician.
Factors that influence TSI results
Different laboratories and assay methods can report TSI in different units and with different cutoffs, so it is important to interpret your result using the reference range on your report. Antibody levels can change over time, including with antithyroid treatment, after pregnancy, or during periods of immune activation. Biotin supplements can interfere with some immunoassays, so tell your clinician and the lab if you take high-dose biotin. Recent treatment changes, iodine exposure (for example, contrast imaging), and the timing of testing relative to symptom onset can also affect how the result fits your overall picture.
What’s included
- Tsi (Thyroid Stimulating Immunoglobulin)
Frequently Asked Questions
What does a positive TSI test mean?
A positive (high) TSI means thyroid-stimulating antibodies were detected. This supports Graves’ disease as a cause of hyperthyroidism, especially if your TSH is low and free T4 and/or free T3 are high. Your clinician will still interpret it with your symptoms, exam, and other labs.
Can you have Graves’ disease with a negative TSI?
Yes, it can happen. Antibody levels can be low early on, fluctuate over time, or be missed depending on the assay. If your thyroid hormones and clinical picture strongly suggest Graves’, your clinician may repeat testing, order TRAb, or consider imaging such as a thyroid uptake scan.
Do I need to fast for a TSI blood test?
Fasting is not usually required for TSI. However, tell your clinician about supplements and medications, especially high-dose biotin, because it can interfere with some immunoassays. If you are combining TSI with other labs (like lipids or glucose), those tests may require fasting.
How is TSI different from TPO antibodies or thyroglobulin antibodies?
TSI targets the TSH receptor and can stimulate the thyroid to produce excess hormone, which fits a Graves’ pattern. TPO antibodies (TPOAb) and thyroglobulin antibodies (TgAb) are more associated with Hashimoto’s thyroiditis and hypothyroidism, although overlap can occur. These tests answer different questions about autoimmune thyroid disease.
When should TSI be rechecked?
Retesting depends on why you tested in the first place. If you are being monitored for Graves’ disease, your clinician may recheck TSI when assessing remission, relapse risk, or changes in symptoms, often alongside TSH and free T4/free T3. If your initial result was borderline or your clinical picture changed, repeating the test after an interval can sometimes clarify the trend.
Can pregnancy affect TSI results?
Yes. Autoimmune thyroid antibodies can change during and after pregnancy, and thyroid-stimulating antibodies are clinically important because they can affect both the pregnant person and, in some situations, the fetus or newborn. If you are pregnant or planning pregnancy, discuss timing and interpretation with your clinician.
What other tests are usually ordered with TSI?
TSI is commonly paired with thyroid function tests such as TSH and free T4, and sometimes free T3. Depending on your history, your clinician may also check other thyroid antibodies (like TPOAb), and in some cases order imaging (ultrasound or uptake scan) to clarify the cause of hyperthyroidism.