Letters Section Editor: Robert M. Golub,
MD, Senior Editor.
In Reply: Dr Scobbo addresses an important
issue in clinical medicine: how to define normal reference values. The statistical
method of determining reference ranges in a group of apparently healthy elderly
patients is prone to bias because there is marked heterogeneity among elderly
persons, it is difficult to distinguish between health and disease in this
population, and disability that is not formally classified as disease is common.
In contrast to a parameter such as hemoglobin levels for which we believe
the normal range should not be adjusted in an older population,1 our
present analyses of thyroid hormone levels indicate that the normal values
of thyrotropin and free thyroxine may need to be redefined in the oldest old
Gussekloo J, de Craen AJM, Westendorp RGJ. Thyroid Status and Survival in Old Age—Reply. JAMA. 2005;293(12):1447-1448. doi:10.1001/jama.293.12.1447-c