TSH Receptor Antibodies (TRAb / TBII)
Antibodies that attach to the thyroid's TSH receptor. They are strongly linked to Graves' disease, an autoimmune cause of an overactive thyroid.
AI-verified against cited sources. Awaiting expert reviewAlso called TRAb, TBII, TSHR AbLOINC 5385-0
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What it is
TSH is the signal from the pituitary gland that tells your thyroid to make hormone. TSH receptor antibodies attach to the same docking site, called the TSH receptor, on thyroid cells. Most of the time in Graves' disease they switch the thyroid on and cause too much hormone. This test measures how much of these antibodies is in your blood. A binding test like this one does not tell whether the antibodies switch the thyroid on or block it.
Why it matters
A positive result helps explain an overactive thyroid and is linked to Graves' disease. A European guideline calls the test a sensitive and specific tool for identifying Graves' hyperthyroidism, and a review of 21 studies found these binding tests had about 97% sensitivity and 98% specificity. It can also be followed during treatment, because levels that stay high are linked to a higher chance of the overactivity coming back. In pregnancy it matters for the baby: the antibodies can cross the placenta and affect the baby's thyroid.
If it’s high
A result above your lab's cutoff means TSH receptor antibodies were found. This is linked to Graves' disease. A binding test cannot tell whether the antibodies stimulate or block the thyroid, so your clinician reads it with your TSH and thyroid hormone levels.
Common causes
- Graves' disease, the most common cause of an overactive thyroid
- Past Graves' disease: antibodies can stay detectable after treatment, including after radioactive iodine or surgery
- Blocking antibodies, which are linked to some cases of an underactive thyroid
What can help
- Ask how this result fits with your TSH, free T4 and free T3
- Ask whether a stimulating-antibody (TSI) test would add anything, since the two tests often give the same answer
- If you are pregnant or planning to be, or have had Graves' disease, tell your prenatal clinician and ask how often the antibodies should be rechecked
- If you are on treatment, ask when the antibodies will be rechecked
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 0–1.75 IU/L. Source: Labcorp, Journal of Clinical Endocrinology & Metabolism.
- Adults (this one applies)0–1.75 IU/L
Sources: Labcorp, Journal of Clinical Endocrinology & Metabolism
If this applies to you
TRAb means a little more for some people. Open the one that fits you.
Thyroid condition
TSH receptor antibodies are the main blood sign of Graves' disease. The European guideline suggests measuring them before antithyroid medicine is stopped, since normal levels go with a better chance of remission, and early in pregnancy for anyone with a history of autoimmune thyroid disease.
What can affect your result
- Test method: binding, bridge and cell-based tests use different cutoffs and are not interchangeable
- Antithyroid drug treatment, which lowers antibody levels over time
- Pregnancy, when levels often fall
- Biotin supplements, on this immunoassay
- Heparin in the sample, or a lipemic or hemolyzed sample
- High-dose biotin can interfere with this immunoassay. Labcorp asks patients to stop biotin at least 72 hours before the draw; check with your clinician or lab first.
- Labcorp rejects samples collected in heparin or from people on heparin therapy, and lipemic or hemolyzed serum.
- Results from different assays are not interchangeable, because cutoffs differ between methods.
- A binding assay cannot tell stimulating antibodies from blocking ones (ETA 2018).
Levels can fall slowly over months of antithyroid treatment, and they can stay detectable after treatment (ETA 2018; Bucci 2017).
When to talk to a clinician
A positive result is not urgent by itself. Talk with a clinician about what it means alongside your TSH and thyroid hormones, especially if you have a fast or uneven heartbeat, shakiness, unplanned weight loss, heat intolerance, bulging eyes or swelling at the front of the neck. If you are pregnant and your result is more than three times your lab's cutoff, your care team usually checks the baby's thyroid more closely. Call 911 or your local emergency number for chest pain, trouble breathing, confusion or fainting.
Questions you could ask
- Which test method does my lab use, and what is its cutoff?
- Will the same lab and method be used each time, so my results can be compared?
- What does this result mean for my thyroid, given my TSH and thyroid hormone levels?
- Do I also need a TSI test, or does this one give the same answer?
- How often should we recheck the antibodies while I am being treated?
- Does this matter for pregnancy plans?
Questions people ask
What is the difference between TRAb and TSI?
TRAb is a binding test. It finds antibodies that attach to the TSH receptor, whether they switch the thyroid on or block it. TSI is a test for the antibodies that switch it on. In a large lab review, the two tests agreed most of the time, so ordering both is often unnecessary.
Does a positive TRAb mean I have Graves' disease?
A positive result supports Graves' disease, especially with a low TSH and high thyroid hormones, but your clinician reads the whole picture. A few other conditions can also give a positive binding test, and a negative result makes Graves' disease less likely but does not rule it out.
Why does TRAb matter in pregnancy?
These antibodies can cross the placenta and affect the baby's thyroid. People with a history of Graves' disease are usually checked early in pregnancy and again around weeks 18 to 22. A level more than three times the lab's cutoff is when extra monitoring of the baby is usually considered.
Show the science and sources
For clinicians and researchers
TSH receptor antibodies (TRAb, also called TSH binding inhibitory immunoglobulins, TBII) include stimulating (TSAb), blocking and neutral antibodies to the TSH receptor. Most current immunoassays are competitive binding assays that detect TBII. They report presence and concentration but not function (ETA 2018). A meta-analysis of 21 studies found pooled sensitivity of 97% and specificity of 98% for second- and third-generation binding assays in Graves' disease (ETA 2018). Labcorp lists an electrochemiluminescence immunoassay with an upper limit of 1.75 units/L. That matches the Roche Elecsys Anti-TSHR assay described by Nelson 2025, a competitive assay in which patient antibody inhibits binding of a labeled monoclonal antibody to the immobilized receptor. The manufacturer cutoff of 1.75 IU/L had 97% sensitivity and 99% specificity in 436 healthy people, 210 with non-Graves thyroid disease and 102 with untreated Graves' disease (Nelson 2025). In a large reference-laboratory review of paired orders, TRAb and a stimulating-antibody bioassay were discordant in 12.5% of pairs and TRAb and a bridge immunoassay in 6.6% (Nelson 2025). TRAb are IgG and cross the placenta. ETA 2018 recommends measuring TRAb at first presentation of pregnancy in people with a history of autoimmune thyroid disease and again at 18 to 22 weeks if raised, and fetal monitoring if the level stays above three times the cutoff. ATA 2017 gives the same threshold (Bucci 2017). ETA 2018 also recommends measuring TRAb before antithyroid drug treatment is stopped (the best course is usually 12 to 18 months), because normal levels indicate a greater chance of remission, and says people whose levels are still high at 12 to 18 months can continue treatment and repeat the test after another 12 months, or consider radioactive iodine or surgery.
LOINC 5385-0 (primary), 57416-0, 40673-6, 82659-4. Specimen: serum.
Sources
- Thyrotropin Receptor Antibody, Serum (test 010314), Labcorp
- TSH Receptor Antibody Test Utilization Patterns From a National Reference Laboratory: TRAb, TSI, or Both?, Journal of Clinical Endocrinology & Metabolism (2025)
- 2018 European Thyroid Association Guideline for the Management of Graves' Hyperthyroidism, European Thyroid Journal (European Thyroid Association) (2018)
- Thyroid-Stimulating Hormone Receptor Antibodies in Pregnancy: Clinical Relevance, Frontiers in Endocrinology (2017)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.