Abstract
Normal values provide the background for interpretation of quantitative imaging data and thus are essential information for daily routine. Nevertheless, the ways how normal values are obtained, presented and interpreted, often do not receive the attention they deserve. We review the concepts of normalcy, the implications of typical normal ranges including the types of distribution of normal data, the possibilities to index for confounding biological factors like body surface area and the limitations of the very concept of normal values, demonstrating that there are no easy statistical solutions for difficult clinical problems.
Highlights
As in all cardiac imaging, normal values form the foundation for interpreting quantitative parameters
While it seems obvious that we can only identify pathologic values if we know the normal range of a parameter, it is easy to become overconfident in the utility and wisdom of normal values
We focus here on the use of normal values in echocardiography, but the same arguments can be made for all imaging modalities
Summary
As in all cardiac imaging, normal values form the foundation for interpreting quantitative parameters. By definition, must be gleaned from a population of ‘normal’, healthy individuals. Meta-analysis studies have been performed utilizing large compilations of normal data from diverse populations, ethnicities and age ranges, for example the EchoNoRMAL study [5, 6] analyzing data from over 22,404 ‘normal’ persons.
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