Is my TSH normal?
Enter your result to see which clinical range it falls into.
Within the standard 0.4–4.5 mIU/L reference range. That range is a population statistic and rises with age — and the popular narrow “optimal TSH” (often quoted as under ~2.0–2.5) is not supported by evidence. Without symptoms or risk factors, a normal TSH is genuinely reassuring.
Reference range and treatment thresholds from the article (AACE/ATA 2012; USPSTF 2015). TSH is a screening test — interpret the pattern (free T4, TPO antibodies, symptoms, age), not this number alone. Estimate for education only — not a diagnosis. Interpret lab results with your clinician.
TSH ranges, and what each one means
These are the same thresholds the interpreter above uses.
| Range | Category | What it means |
|---|---|---|
| < 0.4 mIU/L | Low | Below the reference range — can indicate an overactive (hyper) thyroid. Confirm with free T4/T3; recent illness and biotin supplements can also distort TSH. |
| 0.4–4.5 mIU/L | Normal range | Within the standard 0.4–4.5 mIU/L reference range. That range is a population statistic and rises with age — and the popular narrow “optimal TSH” (often quoted as under ~2.0–2.5) is not supported by evidence. Without symptoms or risk factors, a normal TSH is genuinely reassuring. |
| 4.5–10 mIU/L | Mildly elevated | Subclinical range (4.5–10). Treatment benefit here is uncertain and individualized — more often treated if young, symptomatic, antibody-positive, or pregnant; often just monitored in older adults. Confirm on a repeat with free T4 and TPO antibodies. |
| ≥ 10 mIU/L | Elevated | Above 10 mIU/L — where guidelines establish a clear treatment benefit, especially alongside a low free T4 (overt hypothyroidism). Confirm and interpret with a clinician. |
Where these come from: Reference range and treatment thresholds from the article (AACE/ATA 2012; USPSTF 2015). TSH is a screening test — interpret the pattern (free T4, TPO antibodies, symptoms, age), not this number alone.
Estimate for education only — not a diagnosis. Interpret lab results with your clinician.
The short version
- TSH is the single best first-line screen for thyroid problems, and for most people a normal TSH genuinely is reassuring. But it isn't infallible, and a few specific situations slip past it.
- TSH works backwards from intuition: a high TSH usually means an underactive (hypo) thyroid, and a low TSH means an overactive (hyper) thyroid, because TSH is the pituitary's signal trying to correct the level.
- A normal TSH can miss central hypothyroidism (a pituitary problem, where TSH is normal or low despite low thyroid hormone), early autoimmune disease, and cases where recent illness or biotin supplements distort the result.
- Free T4, free T3, and TPO antibodies add the detail TSH can't: free T4 confirms the actual hormone level, and TPO antibodies identify Hashimoto's, the most common cause of hypothyroidism.
- The 'optimal TSH' narrative overreaches in the other direction. Guidelines do not support treating every mildly abnormal TSH: clear benefit is established mainly when TSH is above 10, and screening asymptomatic adults hasn't been shown to improve outcomes.
- The right approach is targeted: TSH first, add free T4 and TPO antibodies when TSH is abnormal or symptoms and risk factors are present, and interpret the pattern with a clinician — not chase a narrow 'optimal' number.
The full guide
The Thyroid Panel: TSH, Free T4 & Free T3 — and Why a 'Normal TSH' Can Still Miss It
9 min read · Sean Moshrefi, PharmD, MS
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