To The Editor: The study by Dr Gussekloo and
colleagues1 determined that the oldest old
with abnormally high levels of thyrotropin do not experience adverse effects
and may have a prolonged life span. I would like to add an additional conclusion
and a possible study limitation.
“Normal” laboratory result reference ranges are calculated
by either the statistical or epidemiologic method.2 The
more commonly used statistical method defines a reference range as 2 SDs above
and below the mean in a population of apparently disease-free individuals,
usually not stratified by age or sex. In the epidemiologic method, abnormal
values are defined as being associated with adverse consequences.
Scobbo RR. Thyroid Status and Survival in Old Age. JAMA. 2005;293(12):1447–1448. doi:10.1001/jama.293.12.1447-a
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