TRAb optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for TRAb:
- Optimal 0 – 1.75 IU/L (0 – 1.75 U/L); out of range below 0 or above 1.75 IU/L.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| IU/L | 0 – 1.75 | — | below 0 or above 1.75 |
| U/L | 0 – 1.75 | — | below 0 or above 1.75 |
No separate Sufficient band is currently defined for this marker.
What the evidence says
The test that separates Graves' disease from the other causes of thyrotoxicosis, which matters because the treatments diverge. It also crosses the placenta, so a level in a pregnant woman with current or past Graves' disease changes fetal monitoring; the European Thyroid Association advises monitoring the fetus when the level stays above 3 times the assay cut-off. TRAb measures binding and TSI measures stimulation — different assays on different scales, reported under names that are used interchangeably. The band here is the TRAb binding-assay cut-off of 1.75 IU/L used by Labcorp and Mayo. A TSI result has its own cut-off, 0.55 IU/L at the same laboratories, and should be read against the report, not this band.
Assay: Results differ meaningfully between platforms and methods. Compare against the interval printed by the issuing laboratory before acting on a borderline value.
Sources
- Thyrotropin Receptor Antibody, Serum — Labcorp, 2026 · Laboratory / reference-interval sourceReference interval of 0.0 to 1.75 units/L by electrochemiluminescence immunoassay. Sera's acceptable band ends at 2, above this cut-off.
- THYRO - Overview: Thyrotropin Receptor Antibody, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceReference value of 1.75 IU/L or below. A second laboratory with the same cut-off.
- Thyroid-stimulating Immunoglobulin (TSI) — Labcorp, 2026 · Laboratory / reference-interval sourceTSI reference interval of 0.00 to 0.55 IU/L; at that cut-off sensitivity for Graves' disease was 98.6% and specificity 98.5%. A TSI result cannot be scored on the TRAb band.
- FFTSI - Overview: Thyroid-stimulating Immunoglobulin (TSI) — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceTSI reference value of 0.00 to 0.55 IU/L, the same cut-off Labcorp prints.
- 2018 European Thyroid Association Guideline for the Management of Graves' Hyperthyroidism — Kahaly GJ, Bartalena L, Hegedüs L, et al. — European Thyroid Journal (European Thyroid Association), 2018 · Professional societyRecommends TSH receptor antibody measurement for diagnosis and in pregnancy, and expresses its one threshold as more than 3 times the assay cut-off rather than as a number. Supports reading the result against the assay's own cut-off, and the pregnancy point in Sera's note.
What TRAb / TSI (TSH Receptor Antibodies) measures
Antibodies against the TSH receptor, which in Graves' disease stimulate the thyroid rather than block it.
The test that distinguishes Graves' disease from the other causes of thyrotoxicosis, which matters because the treatments diverge completely. Also the marker that guides pregnancy: the antibody crosses the placenta and can affect the fetal thyroid, so a level in a pregnant woman with current or past Graves' changes monitoring. TRAb measures binding and TSI measures stimulation; the two are reported on different scales.