What does a Thyroid-Stimulating Hormone (TSH) level of 0.28 indicate?

Interpretation of TSH Level 0.28

A TSH level of 0.28 mIU/L indicates mild subclinical hyperthyroidism, which requires confirmation with repeat testing and assessment of free T4 and T3 levels before making treatment decisions. 1

Understanding the TSH Value

• A TSH level of 0.28 mIU/L falls below the typical reference range of 0.4-4.5 mIU/L, placing it in the category of "low but detectable" TSH consistent with mild subclinical hyperthyroidism 1, 2
• This value (0.28) falls in the range between 0.1-0.45 mIU/L, which is considered mildly suppressed rather than severely suppressed (<0.1 mIU/L) 1, 2
• A single abnormal TSH value is insufficient for diagnosis and requires confirmation with repeat testing over a 3-6 month interval 1, 3

Diagnostic Approach

• Repeat TSH measurement in 3-6 months to confirm persistent abnormality before making any treatment decisions 1, 2
• Measure free T4 and T3 levels to differentiate between subclinical hyperthyroidism (normal free T4/T3) and overt hyperthyroidism (elevated free T4/T3) 1
• Consider potential non-thyroidal causes of mildly suppressed TSH, including:
  • Medication effects (dopamine, glucocorticoids, amiodarone) 2
  • Normal pregnancy, especially first trimester 2
  • Recovery phase after treatment for hyperthyroidism 2
  • Non-thyroidal illnesses (euthyroid sick syndrome) 2, 3

Clinical Significance and Risks

• For TSH levels between 0.1-0.45 mIU/L (like 0.28):
  • Evidence for increased cardiovascular risk is limited 1
  • Progression to overt hyperthyroidism is unlikely 1, 2
  • About 25% of individuals with subclinical hyperthyroidism revert to a euthyroid state without intervention 1
• Bone health concerns are primarily associated with more suppressed TSH levels (<0.1 mIU/L) rather than mildly suppressed levels like 0.28 1

Management Considerations

• Treatment is typically not recommended for patients with TSH between 0.1 and 0.45 mIU/L 1, 2
• Treatment decisions should consider:
  • Patient age (risks increase in those >60 years) 1, 2
  • Presence of cardiovascular disease or risk factors 1
  • Bone health status, particularly in postmenopausal women 1
  • Presence of hyperthyroid symptoms 2

Important Clinical Pitfalls

• Avoid diagnosing thyroid dysfunction based on a single abnormal TSH value, as this can lead to overdiagnosis and overtreatment 1, 3
• Be aware that TSH secretion has high variability and spontaneous normalization is common, underscoring the importance of confirmatory testing 1
• Low TSH is far more common in older persons than is hyperthyroidism, requiring careful interpretation in this population 4
• When using older (second-generation) TSH assays, correlation between basal and stimulated TSH is weaker, potentially affecting diagnostic accuracy 5