Letters Section Editor: Stephen J. Lurie,
MD, PhD, Senior Editor.
To the Editor: Measurement of the serum thyrotropin
(TSH) concentration is the most sensitive single test of thyroid function.
Concentrations of TSH in the apparently healthy population are log-normally
distributed; 70% to 80% are between 0.3 and 2.0 mIU/L, while 97.5% are less
than 5.0 mIU/L.1 When individuals with thyroid
autoantibodies, goiter, or a strong family history of thyroid disease are
excluded, the upper bound of the 95% TSH concentration reference range decreases
to between 2.5 and 3.0 mIU/L.1,2 It
has been argued that such a "refined normal range" is a better reflection
of thyroid health than a standard population-based reference range and that
elevated values may predict future hypothyroidism.1- 5 This
decreased upper bound would increase the sensitivity of the diagnosis of subtle
hypothyroidism while decreasing its specificity. We investigated the potential
impact of the suggested change in reference range.
Fatourechi V, Klee GG, Grebe SK, Bahn RS, Brennan MD, Hay ID, McIver B, Morris III JC. Effects of Reducing the Upper Limit of Normal TSH Values. JAMA. 2003;290(24):3195-3196. doi:10.1001/jama.290.24.3195-a