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March 23/30, 2005

Thyroid Status and Survival in Old Age

JAMA. 2005;293(12):1447-1448. doi:10.1001/jama.293.12.1447-a

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.

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