Normal TSH Range in Healthy Adults
The normal TSH range for a healthy adult is 0.45-4.5 mIU/L, with a geometric mean of approximately 1.4 mIU/L in disease-free populations. 1
Standard Reference Range
The widely accepted TSH reference range of 0.45-4.5 mIU/L represents the 2.5th to 97.5th percentile derived from the NHANES III study of over 13,000 disease-free individuals who were screened to exclude thyroid disease, thyroid antibodies, and medications affecting thyroid function 1
The geometric mean TSH concentration in healthy populations is approximately 1.4 mIU/L, which represents the central tendency of normal thyroid function 1
A Turkish population study of 408 healthy subjects with normal free T4 and no sonographic abnormalities found a 95% reference interval of 0.38-4.22 mIU/L, with a geometric mean of 1.62 mIU/L and median of 1.40 mIU/L 2
Age-Related Variations
The TSH reference range becomes slightly broader above age 60 years, with values of 0.4-5.9 mIU/L for individuals aged 70-79 years 3
Approximately 12% of persons aged 80+ without thyroid disease have TSH levels >4.5 mIU/L, indicating that age-adjusted reference ranges should be considered in elderly patients 4
The oldest old subjects (>80-85 years) with elevated serum TSH ≤10 mIU/L should be carefully followed with a wait-and-see strategy, generally avoiding hormonal treatment 5
Gender Differences
- The median TSH level is higher in females compared to males, with the 2.5th percentile of TSH lower and 97.5th percentile higher in female subjects 2
Clinical Interpretation Framework
TSH 0.45-4.5 mIU/L: Normal thyroid function 1
TSH <0.45 mIU/L: Suggests subclinical or overt hyperthyroidism; measure free T4 and T3 to distinguish 1
TSH 4.5-10 mIU/L: Indicates subclinical hypothyroidism; measure free T4 and consider thyroid antibodies 1
TSH >10 mIU/L: Generally warrants treatment consideration, particularly if symptomatic 1
Important Caveats
A single abnormal TSH should not trigger immediate diagnosis or treatment due to high TSH variability and frequent reversion to normal without intervention 1
Confirm abnormal values with repeat testing before making treatment decisions, as TSH secretion is pulsatile and variable 1
Exclude non-thyroidal causes of abnormal TSH including acute illness, medications, and recovery from thyroid treatment 1
More than 95% of normal individuals have TSH levels below 2.5 mIU/L, with higher values representing outliers who likely have underlying Hashimoto thyroiditis or other causes of elevated TSH 6
African-Americans with very low incidence of Hashimoto thyroiditis have a mean TSH level of 1.18 mIU/L, strongly suggesting this value is the true normal mean for a normal population 6