What this test measures
TSH receptor antibodies (TRAb) are autoantibodies directed against the TSH receptor on thyroid cells. Most of them are stimulating antibodies that mimic TSH and drive uncontrolled thyroid hormone production — the mechanism of Graves' disease. A minority are blocking antibodies that cause hypothyroidism.
The Thyroid Stimulating Immunoglobulin (TSI) assay is a bioassay that specifically measures stimulating antibodies. The TRAb (or TBII — TSH Binding Inhibitor Immunoglobulin) assay measures both stimulating and blocking activity in a binding-competition test. Both are clinically useful; TRAb is the more widely available immunoassay in Indian labs.
Why it matters
Graves' disease is the commonest cause of hyperthyroidism in India — autoimmune in origin, with a strong female and family-history predisposition. A positive TRAb in a hyperthyroid patient essentially confirms Graves' disease without needing a thyroid uptake scan, which is particularly useful in pregnancy when nuclear imaging is contraindicated.
TRAb levels also predict relapse after antithyroid drug treatment — a persistently positive TRAb at 12–18 months suggests a high recurrence risk, often guiding the decision between continuing medication, radioactive iodine, or surgery. In pregnant women with current or past Graves' disease, a TRAb in the second trimester predicts fetal/neonatal hyperthyroidism risk — high titres warrant fetal monitoring.
How to prepare
No fasting required. Stop biotin / cosmetic supplements 48–72 hours before. Continue antithyroid drugs (carbimazole / propylthiouracil) as usual — TRAb does not need to be checked off treatment.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| TSH Receptor Antibodies (IU/L)[1][2] | < 1.75 IU/L (assay-dependent; some labs report < 1.0) | Negative TRAb makes Graves' disease very unlikely — consider other causes of hyperthyroidism (toxic nodule, subacute thyroiditis, factitious thyrotoxicosis). In a pregnant woman with past Graves', negative TRAb in the second trimester is reassuring against fetal hyperthyroidism. | Positive TRAb in a hyperthyroid patient essentially confirms Graves' disease. A persistently positive TRAb at 12–18 months of antithyroid drug therapy predicts relapse — guides decision-making about continued medication vs. RAI or surgery. Very high TRAb in pregnancy raises fetal/neonatal hyperthyroidism risk. |
TRAb in clinical scenarios
| Scenario | TRAb | Interpretation |
|---|---|---|
| New hyperthyroidism | Positive | Confirms Graves' — start antithyroid drug or RAI |
| New hyperthyroidism | Negative | Likely toxic nodule, thyroiditis or factitious — uptake scan helps |
| Antithyroid drug 12–18 mo | Negative | Reasonable chance of long-term remission off drug |
| Antithyroid drug 12–18 mo | Persistently positive | High relapse risk — consider RAI or surgery |
| Pregnant with past Graves' | Negative (2nd trimester) | Low fetal hyperthyroidism risk |
| Pregnant with past Graves' | Strongly positive | Monitor fetus for goitre and tachycardia |
Frequently asked questions
Why is TRAb tested when I already know I have hyperthyroidism?
To establish the cause. Graves' disease (TRAb positive) is treated differently from a toxic nodule or thyroiditis (TRAb negative). Confirming Graves' lets your doctor pick antithyroid drugs, radioactive iodine or surgery and counsel on remission rates.
Why is TRAb important in pregnancy?
TRAb crosses the placenta. In women with current or past Graves', a TRAb in the second trimester predicts the risk of fetal / neonatal hyperthyroidism — high titres warrant fetal monitoring and sometimes treatment.
I have been on carbimazole for a year — should I stop?
A TRAb at 12–18 months helps decide. If it has fallen and become negative, the chance of long-term remission off the drug is reasonable (about 30–50%). If it remains positive, relapse is likely and definitive treatment (RAI or surgery) may be a better path.
Will TRAb come down with treatment?
In most patients antithyroid drugs both treat the hyperthyroidism and gradually reduce TRAb. After successful definitive treatment (RAI or thyroidectomy), TRAb often persists for years but the gland is no longer there to respond to it.
Can TRAb be raised in Hashimoto's?
TRAb in Hashimoto's is usually the "blocking" type and is positive in a minority. Anti-TPO is the more sensitive marker for Hashimoto's.
Do I need to stop antithyroid drugs before the test?
No. TRAb does not need to be measured off therapy and continuing the drug is safer.
Is TRAb the same as TSI?
They are closely related. TRAb measures both stimulating and blocking antibodies; TSI specifically measures the stimulating activity by bioassay. TRAb is the more widely available test in Indian labs.
Related Hormones / Endocrine tests
Tests commonly ordered alongside TSH RECEPTOR ANTIBODIES, or that help interpret an unexpected result.
Sources & references
- American Thyroid Association — Hyperthyroidism Guideline · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — TSI Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Graves Disease · accessed 2026-05-30T00:00:00.000Z
- Indian Thyroid Society — Consensus · accessed 2026-05-30T00:00:00.000Z
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