How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

A thyroid-stimulating hormone (TSH) blood test is used to check for thyroid gland problems.

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Results are usually available in 2 to 3 days.

High values

High TSH levels may be caused by:

• An underactive thyroid (hypothyroidism). Hashimoto's thyroiditis is the most common cause of primary hypothyroidism.
• A pituitary gland tumor that is making too much TSH. This is uncommon.
• Not taking enough thyroid hormone medicine for treatment of an underactive thyroid gland.

Low values

Low TSH levels may be caused by:

• An overactive thyroid gland (hyperthyroidism). Causes of hyperthyroidism include Graves' disease, a type of goiter (toxic multinodular goiter), or a noncancerous (benign) tumor called a toxic nodule.
• Damage to the pituitary gland that prevents it from making TSH (a condition called secondary hypothyroidism).
• Taking too much thyroid medicine for treatment of an underactive thyroid gland.
• Pregnancy during the first trimester.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking medicine, such as corticosteroids, levodopa, heparin, dopamine, lithium (such as Carbolith or Duralith), methimazole (Tapazole), and propylthiouracil.
• Having had a recent X-ray with iodine dye or test using radioactive materials.
• Having severe stress or a long-term (chronic) illness.