From the Guidelines
Normal TSH levels typically range from 0.4 to 4.0 mIU/L for most adults. TSH is produced by the pituitary gland and regulates thyroid hormone production. When thyroid function is normal, TSH stays within this range. However, during pregnancy, normal TSH levels are generally lower, with first trimester levels typically between 0.1-2.5 mIU/L. For older adults, the upper limit might be slightly higher, sometimes up to 5.0 mIU/L.
Key Considerations
- TSH levels outside the normal range may indicate thyroid disorders - elevated levels suggest hypothyroidism (underactive thyroid), while low levels suggest hyperthyroidism (overactive thyroid) 1.
- Regular monitoring of TSH is important for people with thyroid conditions or those taking thyroid medications to ensure proper dosing and thyroid function.
- The definition of normal TSH levels can vary depending on the population being considered, with average TSH values differing by age, sex, and race/ethnicity 1.
Implications for Clinical Practice
- Clinicians should be aware of subtle signs of thyroid dysfunction, particularly among those at high risk, such as the elderly, postpartum women, and patients with Down syndrome 1.
- Overdiagnosis of thyroid dysfunction is probably common, and many persons labeled with hypothyroidism or hyperthyroidism spontaneously revert to a euthyroid state over time 1.
- Labeling someone with a diagnosis of disease may have adverse psychological consequences, particularly in the case of an otherwise asymptomatic condition 1.
From the Research
Normal TSH Levels
- The normal range for Thyroid-Stimulating Hormone (TSH) levels can vary depending on the laboratory and the individual's age and sex 2.
- According to a study published in 2025, the median TSH level in women was 1.70 mIU/l, with a range of 0.37-6.95 mIU/l 2.
- The study also found that TSH levels decreased slightly with age, with a median TSH level of 1.75 mIU/l in women aged 18-44 years, 1.70 mIU/l in women aged 45-64 years, and 1.64 mIU/l in women aged 65 years and older 2.
- Another study published in 2011 found that the normal range for TSH levels in patients with primary thyroid disease was between 0.20 and 5.64 mIU/l 3.
- It's worth noting that the normal range for TSH levels can vary depending on the laboratory and the individual's specific condition, and that TSH levels should be interpreted in conjunction with other clinical findings and laboratory results 4, 5, 6.
Factors Affecting TSH Levels
- Age: TSH levels may decrease slightly with age 2.
- Sex: TSH levels may vary between men and women, although the exact differences are not well established 2.
- Thyroid disease: TSH levels can be affected by thyroid disease, including hypothyroidism and hyperthyroidism 4, 5.
- Pituitary disease: TSH levels can be affected by pituitary disease, including TSH deficiency 3.
- Levothyroxine treatment: TSH levels can be affected by levothyroxine treatment, and may need to be monitored regularly to ensure optimal replacement therapy 3, 6.