Thyroid tests check how well your thyroid gland, in the front of your neck, is working. The thyroid controls your metabolism, energy, weight, heart rate and temperature.
Why is it done?
They are ordered for tiredness, weight change, hair loss, feeling cold or hot, palpitations, low mood, irregular periods, fertility problems and during pregnancy.
How to prepare
No fasting is needed. Stop biotin supplements 2 to 3 days before testing. If you take levothyroxine, ask whether to take your dose before or after the blood test.
How to read your results
TSH is the first and most sensitive test. A high TSH with low Free T4 means an underactive thyroid; a low TSH with high Free T4 or T3 means an overactive thyroid. Antibodies (anti-TPO) show whether the cause is autoimmune.
Tests in this panel and their normal ranges
| Test | Normal range (adults) |
|---|---|
| TSH (Thyroid Stimulating Hormone) | 0.4–4 mIU/L (0.4–4 µIU/mL) |
| Total T3 | 80–220 ng/dL (1.23–3.4 nmol/L) |
| Anti-TPO Antibodies | Up to 34 IU/mL |
Ranges vary slightly between laboratories. The range printed on your own report is the one to go by.
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This page is for general education and is not a diagnosis. Normal ranges differ between laboratories, so always compare your result with the reference range printed on your own report, and discuss abnormal results with your doctor.