Thyroid Function Testing

Introduction to TSH Tests

The American College of Physicians recommends using highly sensitive TSH tests for screening asymptomatic adults, as they can detect much lower concentrations of TSH, allowing for better detection of hyperthyroidism and subclinical thyroid disorders, with a sensitivity of approximately 98% 1, 2

The American Academy of Family Physicians suggests that for screening asymptomatic adults, the highly sensitive TSH test is the preferred initial test, and values for serum TSH below 0.1 mU/L are considered low, while values above 6.5 mU/L are considered elevated 1, 3
The general reference range for TSH is approximately 0.4 to 4.5 mIU/L, but TSH levels can vary by subpopulations, with up to 12% of persons aged 80 years or older having TSH levels greater than 4.5 mIU/L without evidence of thyroid disease 1

Highly sensitive TSH assays have important limitations, including false positives in hospitalized patients, non-thyroidal illness interference, and medication effects, which can suppress TSH independent of thyroid status 1, 3

Multiple TSH measurements over time provide more reliable diagnostic information than a single test, although this fact is from Praxis Medical Insights, a similar statement can be found in 1, 3, which is preferred, however since 4 is the only one mentioning "multiple measurements" it will be included: Multiple TSH measurements over time provide more reliable diagnostic information than a single test 4