Assay

TSH receptor antibodies

Key Words

Thyroid receptor Ab's, TRA

Specimen Collection

Serum (brown)

Turnaround time

14 days

Test indications

The hyperthyroidism of Grave’s disease is caused by the presence of stimulatory IgG antibodies which bind to thyrotrophin (TSH) receptors on the thyroid follicular cells and cause unregulated stimulation of thyroid hormone production. Such antibodies are detectable in the serum of 85% of patients with Graves'. However this test measures binding to TSH receptors only (both blocking and stimulatory) and thus cannot distinguish between stimulating antibodies in Grave’s disease and inhibiting antibodies in myxoedema. In a patient with known hyperthyroidism where an autoimmune aetiology has been demonstrated by the presence of thyroid microsomal antibodies, measurement of TSH-R Ab is of little additional value. Reports suggesting that high titres of these antibodies predicts early relapse after treatment with antithyroid drugs have not been confirmed. Pregnant women with Graves disease, or that have previously been treated for Graves disease are at risk of having a child with neonatal hypothyroidism.

Methodology

Enzyme Immunoassay

Interferences

None

Reference Range

Negative:  <2.9 IU/L

Equivocal: 2.9-3.3 IU/L

Positive:   >3.3 IU/L

Analytical error

Contact laboratory (x8454)

Reference change value

N/A