Is my TSH (Thyroid Stimulating Hormone) normal?
Free blood test checker · Standard + longevity-optimal ranges
What is a normal TSH level?
TSH controls thyroid hormone production. High TSH signals an underactive thyroid (hypothyroidism) — causing fatigue, weight gain, and cold sensitivity. Low TSH signals overactive (hyperthyroidism). The "normal" range of 0.5-4.5 mIU/L is increasingly contested: data from the National Academy of Clinical Biochemistry shows that over 95% of truly healthy individuals have TSH below 2.5 mIU/L. The original reference cohorts inadvertently included people with undiagnosed autoimmune thyroiditis, inflating the upper limit. This is the "Normal vs. Optimal Paradox" — a TSH of 3.5 mIU/L is technically "normal" but may cause significant symptoms.
| Range | Values |
|---|---|
| Standard Reference | 0.5–4.5 mIU/L |
| Optimal | 0.5–2.5 mIU/L |
| Longevity Optimal | 0.5-2.5 mIU/L |
| High Risk | > 10 mIU/L |
| Low Risk | < 0.3 mIU/L |
What causes abnormal TSH levels?
High TSH (hypothyroidism) is caused by Hashimoto's thyroiditis (autoimmune, ~90% of cases), iodine deficiency, thyroid surgery or radiation, certain medications (lithium, amiodarone), and pituitary disorders. Low TSH (hyperthyroidism) can be caused by Graves' disease, thyroid nodules, excess iodine, or thyroiditis. Stress and poor sleep can also affect TSH levels.
When should you see a doctor?
See your doctor if TSH is above 4.5 mIU/L or below 0.5 mIU/L, if you have symptoms of hypothyroidism (fatigue, weight gain, cold intolerance, dry skin) or hyperthyroidism (anxiety, weight loss, heat intolerance, rapid heartbeat). Request Free T3 and Free T4 testing for a complete picture.
TSH and longevity
Hashimoto's thyroiditis accounts for approximately 90% of all hypothyroid cases and can be detected early via TPO (thyroid peroxidase) and TgAb (thyroglobulin) antibody tests — often years before TSH becomes clinically abnormal. The broad standard range extending to 4.5 mIU/L is increasingly viewed as flawed because the original reference cohorts included individuals with undiagnosed early-stage autoimmune thyroiditis. In aging populations, TSH levels in the upper-normal or mildly elevated range (7.0-9.9 mIU/L) are associated with increased cerebrovascular and cardiovascular mortality. Hypothyroidism also has downstream metabolic effects — it raises LDL and ApoB particle concentrations, connecting thyroid dysfunction directly to cardiovascular risk.
Where to get a TSH test
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Related biomarkers
These biomarkers are often tested alongside TSH for a more complete picture.
Frequently asked questions
What is a normal TSH level?
What does high TSH mean?
Should I also test Free T3 and Free T4?
What is Hashimoto's thyroiditis?
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Sources: Reference ranges based on AHA/ACC, ADA, and AACE clinical guidelines. Biological variation data from Ricos/Westgard database. Longevity-optimal ranges reflect targets used by preventive and functional medicine practitioners.
- A Functional Medicine Approach to Thyroid Hormone Labs — Rupa Health
- Subclinical hypothyroidism and geriatric conditions — PMC
Last reviewed: April 2026. This tool provides general health information and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider about your specific results.