A TSHR (Thyroid Stimulating Hormone Receptor) blood test measures antibodies that interact with the thyroid gland. This diagnostic tool helps healthcare providers assess thyroid health and gain insights into autoimmune conditions, guiding diagnosis and treatment decisions.
What TSHR Antibodies Are
TSHR antibodies are autoantibodies, produced by the immune system mistakenly targeting the body’s own tissues. They target the thyroid stimulating hormone (TSH) receptor on thyroid cells. TSH normally binds to these receptors, prompting the thyroid gland to produce thyroid hormones.
These autoantibodies can have different effects. Some, known as stimulating antibodies (like TSI or thyroid-stimulating immunoglobulins), mimic TSH and overactivate the thyroid gland, leading to excessive hormone production. Other TSHR antibodies, less commonly, can block the receptor, preventing TSH from binding and potentially leading to reduced thyroid hormone production.
Reasons for a TSHR Blood Test
Doctors often order a TSHR blood test when they suspect an autoimmune thyroid condition, particularly Graves’ disease. This disease is the most frequent cause of an overactive thyroid, or hyperthyroidism, and is caused by stimulating TSHR antibodies. Symptoms that might prompt this test include unexplained weight loss, a rapid or irregular heartbeat, anxiety, irritability, heat intolerance, excessive sweating, or an enlarged thyroid gland (goiter).
The TSHR test is also used to confirm Graves’ ophthalmopathy, a condition where the eyes bulge, which is specifically linked to Graves’ disease. Furthermore, it helps monitor the effectiveness of treatment for Graves’ disease, as antibody levels can decrease with successful therapy. It can also assess the risk of passing these antibodies to a fetus during pregnancy.
Interpreting TSHR Test Results
A positive TSHR antibody test, especially for stimulating antibodies (TSI), strongly indicates Graves’ disease, which accounts for over 70% of hyperthyroidism cases. These antibodies bind to the TSH receptors, causing the thyroid gland to produce an excess of thyroid hormones. Elevated levels of TSHR antibodies can also indicate the severity of Graves’ disease and help predict the likelihood of remission or relapse after treatment.
While stimulating antibodies are more common, blocking antibodies can also be detected, though they are less frequently associated with Graves’ disease and can sometimes lead to an underactive thyroid. A negative TSHR antibody result, despite hyperthyroidism symptoms, may prompt further investigation to find other causes of thyroid overactivity, such as toxic nodules. A healthcare professional interprets these results, considering the overall clinical picture and other thyroid hormone levels, to provide an accurate diagnosis and treatment plan.
Preparing for Your TSHR Test
No special preparation, such as fasting, is typically required before the blood draw. However, it is always recommended to follow any specific instructions provided by your doctor or the laboratory. It is important to inform your healthcare provider about any medications or supplements you are taking, as some, like biotin, can potentially affect the test results. The test itself involves a standard blood draw, where a healthcare professional collects a blood sample from a vein, usually in your arm.