What Is a Normal TSH Level?
The normal TSH range is 0.4–4.0 mIU/L. Values below or above this range may indicate a condition that requires further evaluation.
Reference Range Table
| Marker | Low | Normal | High |
|---|---|---|---|
| TSH | Below 0.4 mIU/L — possible hyperthyroidism | 0.4–4.0 mIU/L | Above 4.0 mIU/L — possible hypothyroidism |
What Affects Your Results
Time of day (TSH is highest in early morning), severe illness, certain medications (biotin supplements, steroids, dopamine), pregnancy, and recent changes to thyroid medication can all affect TSH levels.
When to Retest
If adjusting thyroid medication, retest in 6-8 weeks. Once stable, every 6-12 months. For routine screening, annually after age 35.
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