Author: MAI Medical Information Team ·
Updated: 2026-04-15 ·
Reviewed by: Medical Information Team ·
Sources: WHO, UpToDate, PubMed
Thyroid Tests Explained: TSH, T3, T4 Normal Ranges
What Are Thyroid Tests?
Thyroid blood tests measure hormones produced by the thyroid gland — a small butterfly-shaped gland in the front of your neck. The main tests are TSH (Thyroid Stimulating Hormone), Free T4 (FT4), and Free T3 (FT3). These hormones regulate metabolism, energy, heart rate, and body temperature.
Thyroid Test Normal Ranges
| Test | Normal Range | High = ? | Low = ? |
|---|---|---|---|
| TSH | 0.4–4.0 mIU/L | Hypothyroidism | Hyperthyroidism |
| Free T4 | 12–22 pmol/L | Hyperthyroidism | Hypothyroidism |
| Free T3 | 3.1–6.8 pmol/L | Hyperthyroidism | Hypothyroidism |
Hypothyroidism vs Hyperthyroidism
Hypothyroidism (underactive thyroid): fatigue, weight gain, dry skin, hair loss, feeling cold. TSH is high, FT4 is low.
Hyperthyroidism (overactive thyroid): weight loss, anxiety, rapid heartbeat, sweating, insomnia. TSH is low, FT4/FT3 are high.
MAI Tip: Upload your thyroid test results to MAI — our AI will explain what your TSH, T3, and T4 levels mean and whether you should see an endocrinologist.
⚠️ Important: This article is for informational purposes only and does not constitute medical advice.
Always consult your doctor before making health decisions.
Sources: World Health Organization (WHO), UpToDate Clinical Reference, PubMed Medical Research Database.
Sources: World Health Organization (WHO), UpToDate Clinical Reference, PubMed Medical Research Database.
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