Laboratory Test Reference Guide

Frozen

≤ 2.0 IU/L

In untreated patients with Graves’ disease, the sensitivity of TRAb to detect Graves disease is 97% and specificity is 99%.

Performance in patients with subclinical hyperthyroidism is not well known.

This 3^rd generation TSH receptor antibody assay (TRAb) detects both stimulating and blocking antibodies; the test should ONLY be performed in patients with hyperthyroidism. In a patient with hyperthyroidism and positive TRAb, the antibodies are stimulating. Over time these antibodies (which are polyclonal) may change from stimulating to blocking. A mixture of stimulating and blocking antibodies may be present, resulting in a “balanced” effect on thyroid function (= euthyroid).

The test is very helpful in distinguishing Graves’ disease from other causes of hyperthyroidism. However, antibodies may be present in 5 – 15% of patients with subacute painless thyroiditis or postpartum thyroiditis.

The test is also helpful in predicting short term relapse when stopping anti-thyroid medication; risk is low if titre is low (say < 4) and high if titre is high. Due to the long term relapsing nature of Graves’ disease, a current low titre does not exclude a relapse in the long term.

Euthyroid Graves’ Ophthamopathy is a rare condition. While a positive TRAb suggests the diagnosis, the performance of the assay in this setting is not well known, therefore interpretation is best left for specialists such as endocrinologists and ophthalmologists.

Measuring TRAb is informative in pregnant patients with a history of Graves' disease, without a thyroid (e.g. following radioactive iodine, thyroidectomy) or taking antithyroid medication  – if TRAb is present, the antibodies can cross the placenta and act on the foetal thyroid.  Suggest checking TRAb  before 24 – 28 weeks gestation, and if raised, specialist review is recommended.

Amiodarone induced hyperthyroidism – interpretation of TRAb is complicated and best left for specialists such as endocrinologists.

0.2 mL serum