TSH optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for TSH:
- Optimal 0.5 – 2 mIU/L (0.5 – 2 μIU/mL); sufficient 0.5 – 4.5 mIU/L (0.5 – 4.5 μIU/mL); out of range below 0.5 or above 4.5 mIU/L.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mIU/L | 0.5 – 2 | 0.5 – 4.5 | below 0.5 or above 4.5 |
| μIU/mL | 0.5 – 2 | 0.5 – 4.5 | below 0.5 or above 4.5 |
What the evidence says
The acceptable band is the traditional TSH reference range of 0.5 to 4.5 mIU/L, as the American Thyroid Association describes it. Laboratories print slightly different limits for their own assay, from about 0.3 to 0.45 at the bottom and 4.2 to 5.3 at the top, so check a borderline result against the issuing laboratory's interval. The narrower optimal band ending at 2 is a functional target with no guideline behind it; in pooled cohort data on 134,000 adults the lowest cardiovascular and mortality risk sat at a TSH of roughly 1.9 to 2.9, not below 2. TSH also follows a daily rhythm, running highest overnight and early morning.
Sources
- Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement — Jonklaas J, Bianco AC, Bauer AJ, et al. — Thyroid (American Thyroid Association), 2014 · Professional societyDescribes the traditional TSH reference range for the general population as 0.5 to 4.5 mIU/L, which is Sera's acceptable band exactly. Elsewhere it gives 0.4 to 4.0 mIU/L as the treatment target range. Published 2014; a search found no later ATA hypothyroidism guideline for non-pregnant adults, so it is cited as the edition in force.
- Thyroid-stimulating Hormone (TSH) — Labcorp, 2026 · Laboratory / reference-interval sourceReference interval for anyone over 10 years: 0.450 to 4.500 μIU/mL. Matches Sera's upper edge of 4.5; the lower limit is 0.45 against Sera's 0.5.
- STSH - Overview: Thyroid-Stimulating Hormone-Sensitive (s-TSH), Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdult reference values of 0.3 to 4.2 mIU/L from age 20. A slightly lower interval than Sera's on both sides, showing the edges move with the assay.
- Thyroid Function Tests — North Bristol NHS Trust, Severn Pathology, 2026 · Laboratory / reference-interval sourceUK laboratory interval: TSH 0.38 to 5.33 mU/L, free T4 8.0 to 18.0 pmol/L, free T3 3.7 to 6.6 pmol/L. Its TSH upper limit is higher than Sera's 4.5.
- The optimal healthy ranges of thyroid function defined by the risk of cardiovascular disease and mortality: systematic review and individual participant data meta-analysis — Xu Y, Derakhshan A, Hysaj O, et al. — The Lancet Diabetes & Endocrinology, 2023 · Peer-reviewed publicationPooled individual data on 134,346 adults. Cardiovascular and mortality risk was lowest between the 60th and 80th percentiles of TSH, with medians of 1.90 and 2.90 mIU/L, and the lowest fifth of TSH carried higher all-cause mortality. This does not support an optimal band that stops at 2.0.
What TSH (Thyroid-Stimulating Hormone) measures
A hormone made by the pituitary gland in your brain that tells the thyroid how much hormone to produce.
TSH is the main first-line test for thyroid problems. High levels usually mean the thyroid is underactive, and low levels can mean it is overactive.