Types of Reference Values

In practice it is often necessary or convenient to give a short description associated with the term reference values, such as health-associated reference values (close to what was understood by the obsolete term normal values). Other examples of such qualifying words are diabetic, hospitalized diabetic, and ambulatory diabetic. These short descriptions prevent the common misunderstanding that reference values are associated only with health. 

We may further distinguish between subject-based and population-based reference values, SuhjecCbased reference values are previous values from the same individual, obtained when he or she was in a known state of health. Population-based reference values are those obtained from a group of well-defined reference individuals and are usually the type of values referred to when the term reference values is used without any qualifying words. This chapter deals primarily with population-based values. 

The body of this chapter discusses population-based univariate reference values and quantities derived from them. If, for example, we produce, treat, and use separate reference values for cholesterol and triglycerides in serum, we have two sets of univariate reference values. The term multivariate 

Certain conditions apply for a valid comparison between a patient s laboratory results with reference values  

AH groups of reference individuals should be clearly defined. 

---

Three types of reference-value comparisons are used to evaluate trend data baseline data, rate of change, and industrial standards. 

The DRIs consist of four components. Each type of reference value is calculated from daily intakes averaged over time (usually one or more weeks). The surveys include, but are not limited to, (l)random selection of healthy individuals and asking them to either report what they have eaten or to maintain food diaries, (2) monitoring overall food production and consumption, and (3) correlating a defined population s health status with the group s food intake. Sometimes the results from the surveys are correlated with the type of assays listed in Table 8.2. The four Dietary Reference Intakes are ... 

Examples for reference materials useful for instrument calibration, method validation and development in the field of human materials for which certified or other kinds of concentration values are reported for the 13 trace elements considered in this book (Al, As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Se, Tl, V and Zn) are given in Table 3. The data are taken from the survey prepared by Cortes Toro et al. (1990) and from other sources (BCR, 1992, Trahey, 1992, Chai Chifang, 1993) which the reader should consult for further details. Most of the columns are self explanatory. Column T contains a code (C = certified, N = noncertified or information value) for the type of reference value specified by the issuing authority. The uncertainty in the concentration value is expressed as a percentage error, but the meaning of this may differ somewhat from one material to another. In most cases it expresses the 95% confidence interval of the mean, but in a few other cases a tolerance interval, or some other definition (sometimes unspecified), may have been used by the producer. 

---