Alternative names 
TSH receptor antibody; TSI

Definition
TSI is a test that measures the amount of TSI antibody in the blood.

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to fill with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The tourniquet is then removed to restore circulation. After blood has been collected the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test
No special preparation is usually necessary.

Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

 
• Infant test or procedure preparation (birth to 1 year)  
• Toddler test or procedure preparation (1 to 3 years)  
• Preschooler test or procedure preparation (3 to 6 years)  
• School age test or procedure preparation (6 to 12 years)  
• Adolescent test or procedure preparation (12 to 18 years)

How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed
This test may be performed as part of the diagnostic work-up of Graves’ disease.

The TSI is an antibody directed against the receptor for TSH on the thyroid gland. This antibody interacts with the receptor and mimics the action of the pituitary hormone TSH. The TSI stimulates the gland to secrete excessive amounts of thyroid hormone. TSI measurements are also performed in the third trimester of pregnancy to predict neonatal Graves’ disease.

Normal Values

Normal Values are less than 130 % of basal activity. Normal value ranges may vary slightly among different laboratories.

What abnormal results mean

Greater-than-normal levels may indicate:

 
• Graves’ disease  
• Hashitoxicosis  
• Neonatal thyrotoxicosis

What the risks are

 
• Excessive bleeding  
• Fainting or feeling lightheaded  
• Hematoma (blood accumulating under the skin)  
• Infection (a slight risk any time the skin is broken)  
• Multiple punctures to locate veins

Special considerations
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Medical Encyclopedia

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.