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The normal range: it is not normal and it is not a range
  1. Martin Brunel Whyte1,2,
  2. Philip Kelly1
  1. 1 Department of Medicine, King’s College Hospital NHS Foundation Trust, London, UK
  2. 2 Department of Clinical & Experimental Medicine, University of Surrey, London, UK
  1. Correspondence to Dr Martin Brunel Whyte, Department of Medicine, King’s College Hospital NHS Foundation Trust, London SE5 9RS, UK; m.b.whyte{at}surrey.ac.uk

Abstract

The NHS ‘Choose Wisely’ campaign places greater emphasis on the clinician-patient dialogue. Patients are often in receipt of their laboratory data and want to know whether they are normal. But what is meant by normal? Comparator data, to a measured value, are colloquially known as the ‘normal range’. It is often assumed that a result outside this limit signals disease and a result within health. However, this range is correctly termed the ‘reference interval’. The clinical risk from a measured value is continuous, not binary. The reference interval provides a point of reference against which to interpret an individual’s results—rather than defining normality itself. This article discusses the theory of normality—and describes that it is relative and situational. The concept of normality being not an absolute state influenced the development of the reference interval. We conclude with suggestions to optimise the use and interpretation of the reference interval, thereby facilitating greater patient understanding.

  • normality
  • biological variation
  • mean

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0

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Footnotes

  • Contributors MBW and PK contributed jointly to the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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