To the Editor,
There still appears a controversial use of the two terms reference interval and reference range. R. Dybkaer (former International Federation of Clinical Chemistry and Laboratory Medicine [IFCC] president) and HE Solberg have published an approved IFCC recommendation [1] in which they state under Top 2.2:
“A widely used practice is to state the limits of an interval7) that depends on location and dispersion of the reference values. In clinical chemistry and haematology it is customary to calculate a closed interval comprising a central number fraction of 0.95 (or 95 per cent) of the reference values. Other number of fractions or an asymmetrical position of the reference interval may be more appropriate in particular cases.
7) The term ‘interval’ is preferred to ‘range’ which should be restricted to the difference between upper and lower limit of an interval (or class).”
According to this recommendation, the reference interval for sodium concentration in serum or plasma would be, e.g. 135–145 mmol/L and the reference range would be 10 mmol/L. In statistics, range may also be called span (the difference between two limits, resp. two numbers).
This approved recommendation is still valid and is widely recognized internationally [2], [3]. The limits of the reference interval may be called lower and upper reference limit and are often given with 90% confidence limits.
Translation into other languages may sometimes be problematic. For instance, both the terms “interval” and “range” can be translated to “Bereich” in the German language. For didactical reasons and in analogy to the aforementioned international usage, we recommend for German-speaking countries, the usage of “ReferenzIntervall” for reference interval. The lower and upper reference limit (abbreviated lRL and uRL) can be translated to “untere” and “obere Referenzgrenze” (uRG and oRG). The term normal range (“Normalbereich”) should not be used anymore because normality is difficult to be defined in medicine [4], [5].
Research funding: None declared.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Authors state no conflict of interest.
Ethical approval: Not applicable.
References
1. Dybkaer R, Solberg HE. Presentation of observed values related to reference values. J Clin Chem Clin Biochem 1987;25:657–62.Search in Google Scholar
2. Jones GR, Haeckel R, Loh TP, Sikaris K, Streichert Th, Katayev A, et al. Indirect methods for reference interval determination – review and recommendations. On behalf of the IFCC Committee on Reference Intervals and Decision Limits. Clin Chem Lab Med 2019;57:20–9.10.1515/cclm-2018-0073Search in Google Scholar PubMed
3. Ozarda Y, Sikaris K, Streichert T, Macri J. Distinguishing reference intervals and clinical decision limits – a review by the IFCC Committee on Reference Intervals and Decision Limits. IFCC Committee on Reference intervals and Decision Limits (C-RIDL). Crit Rev Clin Lab Sci 2018;55:420–31.10.1080/10408363.2018.1482256Search in Google Scholar PubMed
4. Grasbeck R. The evolution of the reference value concept. Clin Chem Lab Med 2004;42:692–7.10.1515/CCLM.2004.118Search in Google Scholar PubMed
5. Haeckel R. Wosniok W, Arzideh F. A plea for intra-laboratory reference limits. Clin Chem Lab Med 2007;45:1033–42.10.1515/CCLM.2007.249Search in Google Scholar
©2020 Rainer Haeckel et al., published by De Gruyter, Berlin/Boston
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