The Antibody Found in Graves' Disease
The primary antibody found in Graves' disease is thyroid-stimulating immunoglobulin (TSI), which is a type of TSH receptor antibody (TRAb) that stimulates the thyroid gland by binding to the TSH receptor. 1, 2
Types of TSH Receptor Antibodies in Graves' Disease
- Thyroid-stimulating immunoglobulin (TSI): The primary pathogenic antibody that mimics TSH action by binding to and activating the TSH receptor, causing hyperthyroidism
- TSH-binding inhibitor immunoglobulin (TBII): Another type of TRAb that can be measured in Graves' disease
Both TSI and TBII are collectively referred to as TSH receptor antibodies (TRAb) and are present in the vast majority of patients with Graves' disease. Studies have shown that approximately 92% of untreated Graves' patients have both positive TSI and TBII, and virtually all Graves' patients (100%) have at least one type of TRAb (either TSI or TBII) 2.
Clinical Significance of TRAb Testing
TRAb testing has important clinical applications:
- Diagnostic value: TRAb tests have >95% sensitivity and specificity for diagnosing Graves' disease 3
- Monitoring treatment response: TRAb levels typically decrease during successful antithyroid drug therapy 4
- Predicting relapse: TRAb levels can predict the likelihood of remission or relapse after treatment
When to Test for TRAb
Guidelines recommend considering TRAb testing in the following scenarios:
- When clinical features suggest Graves' disease, particularly with ophthalmopathy 5
- To differentiate Graves' disease from other causes of hyperthyroidism
- To monitor disease activity and treatment response
- In pregnant women with current or previous Graves' disease (TRAb ≥5 IU/L indicates increased risk of fetal/neonatal thyrotoxicosis) 3
Cautions in TRAb Interpretation
- Mildly elevated TRAb may occasionally be present in patients with transient thyrotoxicosis not due to Graves' disease 6
- TRAb levels increase for about a year following radioactive iodine therapy before gradually declining 3
- The pattern of TRAb changes during treatment varies between patients and can help predict outcomes 4
Other Thyroid Antibodies in Graves' Disease
While TRAb is the pathogenic antibody in Graves' disease, other thyroid autoantibodies may also be present:
- Anti-thyroglobulin antibody (AbTG)
- Anti-thyroid peroxidase antibody (AbTPO)
- Anti-thyroid microsomal antibody (ATMA)
These antibodies are more commonly associated with Hashimoto's thyroiditis but can also be found in Graves' disease patients 5.
By understanding the role of TSI/TRAb in Graves' disease, clinicians can make more informed decisions about diagnosis, treatment selection, and monitoring of patients with this autoimmune thyroid disorder.