TSH receptor antibodies (TRAb) test

TSH receptor antibodies (TRAb) are autoantibodies that attach to the thyrotropin (TSH) receptors on thyroid cells. Some of these antibodies — thyroid-stimulating immunoglobulins (TSI) — mimic the action of TSH and push the thyroid into making too much hormone, even when the natural TSH level is low. This is the main mechanism of Graves' disease (diffuse toxic goitre). The test is done on a venous blood sample. According to MedlinePlus, TRAb are usually tested together with other thyroid antibodies — thyroid peroxidase antibodies (anti-TPO) and thyroglobulin antibodies (anti-Tg) — in order to establish whether a thyroid function disorder is caused by an autoimmune process. Unlike TSH or free thyroxine, which show how much hormone is circulating in the blood at the moment, TRAb/TSI show whether the body is producing antibodies that act on the thyroid control mechanism itself.

• When a laboratory test shows hyperthyroidism (a low TSH, a raised free T4 and/or T3) and the cause needs to be established
• When Graves' disease is suspected — with signs such as weight loss, a fast heartbeat, heat intolerance, insomnia, anxiety, hand tremor, goitre
• When there are bulging eyes or other eye symptoms typical of Graves' ophthalmopathy
• In late pregnancy, for women who have had or who have Graves' disease — to assess the risk to the newborn
• When a radioactive iodine uptake test is not possible or not suitable for establishing the cause of hyperthyroidism

Raised TSH receptor antibodies (especially TSI) are considered a sign of Graves' disease. According to MedlinePlus, rarer causes are hashitoxicosis and neonatal thyrotoxicosis. The more antibodies are detected, the higher the likelihood that autoimmune thyroid disease is present.

Possible causes of a raised result

• Graves' disease (diffuse toxic goitre) — the most common cause of raised TRAb/TSI
• Hashitoxicosis — a temporary hyperthyroid phase in autoimmune thyroid disease
• Neonatal thyrotoxicosis — when maternal antibodies cross the placenta to the fetus

Symptoms that may accompany a raised result

• Weight loss
• Bulging eyes (exophthalmos)
• Hand tremor
• Heat intolerance
• Insomnia
• Anxiety
• A fast heartbeat
• Goitre

What to discuss with a doctor

• TSH and free T4/T3 — to assess whether hyperthyroidism is already present and how pronounced it is
• Other thyroid antibodies (anti-TPO, anti-Tg) — to distinguish Graves' disease from other autoimmune conditions
• An assessment of eye symptoms, if Graves' ophthalmopathy is suspected
• For pregnant women — to discuss the risk to the newborn with a doctor in late pregnancy

How TRAb differ from anti-TPO and anti-Tg

Anti-TPO and anti-Tg are more often linked to Hashimoto's disease (hypothyroidism), while TRAb — and especially TSI — are linked to Graves' disease (hyperthyroidism). All three belong to the group of thyroid antibodies and are often tested together, so that the cause of the autoimmune process is clearer.