TSH test

What the test is

High TSH usually means the thyroid is underactive; low TSH usually means it's overactive.

Biotin supplements can interfere with thyroid tests; ask whether to stop them a few days before.

Why it's done

• Tiredness, weight changes, feeling cold or hot, hair loss, or a fast heartbeat
• Checking thyroid medicine doses
• Pregnancy planning or pregnancy with thyroid risk

Getting ready and what happens

• No fasting is needed.
• Ask about stopping biotin 2 to 3 days before.
• If you take levothyroxine, ask whether to take it before or after the test.

How the test is done

• A health worker cleans the skin, puts a band around your arm, and draws blood from a vein with a small needle. It takes a few minutes.

What the results mean

Normal ranges vary from lab to lab and can differ by age, sex, and pregnancy. Your report lists your lab's own range next to each result. A result a little outside the range is often not a problem.

High TSH

Usually means an underactive thyroid (hypothyroidism). Mildly high results are often rechecked with a free T4 test.

Low TSH

Usually means an overactive thyroid or too much thyroid medicine.

Questions to ask your provider

• What do my results mean for me?
• Do I need to repeat this test or have other tests?
• Do I need a free T4 or antibody test?
• Should my thyroid medicine dose change?

Risks

A blood draw is very safe. You may have slight pain or a small bruise where the needle went in.

Related conditions

• Underactive thyroid (hypothyroidism)
• Overactive thyroid (hyperthyroidism)
• Goiter (enlarged thyroid)
• Thyroid nodule or thyroid cancer (needs checking)

Related medicines

• Levothyroxine
• Methimazole

Related tests

• Free T4 test