Effects of Biological and Analytical Variations on the Appropriate Use of “Reference Intervals” in Clinical Chemistry. Proposal of a Scheine for Longitudinal Assessment of Laboratory Values

Abstract

For 21 different laboratory parameters the separate contributions of both biological (age, sex, hospitalization) and analytical variations to the total variation were examined. For each of the different laboratory parameters, the reference interval and critical difference are given for the longitudinal evaluation of analysis results. These critical differences are not only calculated on the basis of the analytical imprecision from day to day, as has been usual until now, but the mean individual deviations of the reference samples are included. The critical differences given in this paper are therefore essentially higher for some parameters compared with the critical differences on the basis of the analytical deviation, and are much more realistic quantities to be used for longitudinal evaluation. Finally, for practical purposes, a scheme is presented for use with longitudinal assessment of laboratory values, in order to enable the practicing physician to consider these data in daily decision making.