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Alternate Names

  • thyroid stimulating immunoglobulin
  • thyroid receptor antibody
  • LATS
  • TSIG
  • long-acting thyroid stimulator


This test measures the level of thyroid stimulating immunoglobulin (TSI) in the blood. A healthcare professional can use this test to find out if a condition called Graves' Disease is causing a person's hyperthyroidism.

Who is a candidate for the test?

This test is normally performed to diagnose and evaluate suspected thyroid disease. It may also be used to monitor treatment of certain thyroid disorders.

How is the test performed?

To measure the amount of TSI in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or "tourniquet," is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them.
A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.

What is involved in preparation for the test?

A person should request specific instructions from his or her healthcare professional.

What do the test results mean?

Normally, there is no TSI in the blood. If TSI is found in the blood, this indicates that this abnormal antibody is responsible for causing the person's hyperthyroidism.

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