What is the antibody test for hyperthyroidism (Graves' disease)?

From the Guidelines

The primary antibody test for hyperthyroidism is the thyroid stimulating immunoglobulin (TSI) or thyroid stimulating hormone receptor antibody (TRAb) test, which is most useful for diagnosing Graves' disease, the most common cause of hyperthyroidism. These antibodies mimic thyroid stimulating hormone (TSH) by binding to TSH receptors on the thyroid gland, causing excessive thyroid hormone production. Other important antibody tests include thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb), which are often present in autoimmune thyroid conditions. When ordering these tests, they should be interpreted alongside thyroid function tests including TSH, free T4, and free T3 levels for a comprehensive evaluation. Antibody testing is particularly valuable when the diagnosis is unclear from clinical presentation and basic thyroid function tests alone, or when trying to determine the specific cause of hyperthyroidism. The presence of these antibodies not only confirms the autoimmune nature of the condition but may also help predict disease course and treatment response. Testing should be performed before initiating treatment when possible, as some therapies can affect antibody levels 1.

Key Points

• The TSI or TRAb test is the primary antibody test for hyperthyroidism
• Other important antibody tests include TPOAb and TgAb
• Antibody testing should be interpreted alongside thyroid function tests
• Testing should be performed before initiating treatment when possible
• The presence of antibodies can help predict disease course and treatment response

Recommendations

• Order TSI or TRAb test for patients with suspected hyperthyroidism
• Interpret antibody test results alongside thyroid function tests
• Perform antibody testing before initiating treatment when possible
• Consider the presence of antibodies when predicting disease course and treatment response

From the Research

Antibody Tests for Hyperthyroidism

• The diagnosis of hyperthyroidism typically involves biochemical tests, such as low TSH, high free thyroxine (FT4), or high free tri-iodothyonine (FT3) 2.
• Once hyperthyroidism is confirmed, a nosological diagnosis is necessary to determine the underlying cause, with helpful tools including TSH-receptor antibodies, thyroid peroxidase antibodies, thyroid ultrasonography, and scintigraphy 2.
• Thyroid-stimulating immunoglobulin (TSI) and thyrotropin receptor antibodies (TRAb) are used to diagnose Graves' disease, a common cause of hyperthyroidism, with studies showing excellent diagnostic performance for TSI and TRAb 3, 4.

Diagnostic Performance of TSI and TRAb

• A study evaluating the diagnostic performance of TSI and TRAb for Graves' disease found that TRAb had an area under the curve (AUC) of 0.981 and a clinical cut-off value of 1.245 IU/L, with a sensitivity of 96.6% and specificity of 97.1% 3.
• The same study found that TSI had an AUC of 0.992 and a clinical cut-off value of 0.467 IU/L, with a sensitivity of 98.8% and specificity of 96.4% 3.
• Another study comparing the diagnostic accuracy of TSI and TBII assays found that both tests showed similar performance in differentiating Graves' disease from other causes of thyrotoxicosis, with a strong positive correlation between the two tests 4.

Treatment and Management

• The treatment of hyperthyroidism depends on the underlying cause, with options including antithyroid drugs, radioactive iodine ablation, and surgery 2, 5, 6.
• Graves' disease is typically treated with antithyroid drugs, with long-term treatment (5-10 years) associated with fewer recurrences than short-term treatment (12-18 months) 2.
• Toxic nodular goitre is often treated with radioiodine (131I) or thyroidectomy, while destructive thyrotoxicosis is usually mild and transient, requiring steroids only in severe cases 2.