The choice of 95% is arbitrary, though widely accepted internationally.    I believe it was originally proposed by an IFCC working group in 1987:  Solberg, HE International Federation of Clinical Chemistry (IFCC). Scientific Committee, Clinical Section. Expert Panel on Theory of Reference Values (EPTRV) International Committee for Standardization in Haematology (ICSH), Standing Committee on Reference Values . Approved recommendation (1987) on the theory of reference values. Part 5. Statistical treatment of collected reference values. Determination of reference limits. J Clin Chem Clin Biochem 1987;25:645–56. (Clin Chim Acta 1987;170:S13–32).

 

An argument could certainly be constructed for the use of  a different basis to determine reference intervals;  moving to 99% would significantly widen many reference intervals, with clinical consequences and risks (both positive and negative).   It would require considerable work by manufacturers and would be associated with significant costs, in addition to the need to educate clinicians. 

 

There is a good article from the Annals in 2012 which summarises the relevant history and some of the issues (https://journals.sagepub.com/doi/full/10.1258/acb.2008.008170).  Thinking around the use of big data approaches has probably moved on since this was published, and a comparison of different approaches is currently one of the projects of an IFCC committee (http://www.ifcc.org/ifcc-scientific-division/sd-committees/c-ridl/).

 

Best wishes

Ian

 

 

Ian S.Young

 

Professor of Medicine, Queen’s University Belfast

 

 

 

 

 

 

Traditionally, our reference interval contains 95% of a “normal” population.  Why are we using that, and not using a reference interval that contains 99% of the “normal” population?

 

Martin

 

ps. I use the paper below for teaching

 

https://jada.ada.org/article/S0002-8177(14)60171-9/pdf

 

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