Thyroid Function Test (TFT): normal range & what your result means
The TFT checks your thyroid — the gland that sets your metabolism — mainly through TSH, with free T4 and T3 as needed.
Typical adult reference range
| Measure | Range |
|---|
| TSH | 0.4–4.0 mIU/L |
| Free T4 | 0.8–1.8 ng/dL |
| Free T3 | 2.3–4.2 pg/mL |
What a HIGH result can mean
- High TSH usually means an UNDER-active thyroid (hypothyroidism): tiredness, weight gain, cold intolerance
- Low TSH with high T4/T3 means an OVER-active thyroid
What a LOW result can mean
- Low TSH usually means an OVER-active thyroid (hyperthyroidism): weight loss, palpitations, heat intolerance
Ranges vary by lab. Reference ranges are TYPICAL ADULT values and vary by laboratory, age, sex, pregnancy and the method used. Always read your result against the range printed on YOUR report, and let your doctor interpret it alongside your history.
Frequently asked questions
What does a high TSH mean?
A high TSH usually signals an underactive thyroid — your gland needs more stimulation. Symptoms include tiredness, weight gain and feeling cold. Your doctor may start thyroid hormone.
Do I need to fast for a thyroid test?
Usually no. For consistency, many people test in the morning; if you take thyroid medicine, ask whether to take it before or after the blood draw.
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MedDroid is an AI medical assistant and can make mistakes. It provides general health information, not a diagnosis or medical advice — always consult a qualified clinician. In an emergency, contact your local emergency number immediately.