Abstract
Thyroid function is most often monitored clinically through measurement of the regulatory hormone, thyrotropin (TSH). Subclinical hypothyroidism is generally defined as a TSH level above the reference range while thyroid hormone levels remain within the reference range. Elevated TSH is more common among older adults, leading to high rates of treatment, and over-treatment, in this population. However, the use of levothyroxine in older adults with mild TSH elevations has begun to be called into question by observations that demonstrate a lack of harm from not treating and a lack of benefit from treating. Importantly, these findings suggest that the existing diagnostic algorithm for subclinical hypothyroidism, based on isolated TSH elevation, may be inappropriate for older adults. Age-specific reference ranges have been suggested as a way to avoid inappropriate treatment, but that strategy continues to rely on population norms rather than disease definitions to drive clinical decisions. Recent insight into age-related variability in the underlying pathophysiology that impacts on thyroid function tests demonstrates the need for new clinical tools to allow the targeted use of therapy where it will have benefit.