Biological Variability of 26 Clinical Chemistry Analytes

Analytical, within-subject, and between-subject components of variation were estimated for 26 clinical chemistry analytes from duplicate analyses of 10 specimens collected from 27 healthy elderly subjects over a period of 20 weeks. Within-subject variations were similar to those generated previously by us in younger subjects. We conclude, therefore, that homeostasis is not compromised by age alone, and biologi-cal variability does not increase simply with age. All analytes except serum water had marked individuality, showing that conventional population-based reference values are of limit-ed utility.The critical differences required for two results to be significantly (P 0.05) changed are not the same as those that prompt action by clinicians. Although heterogeneity of within-subject variation does exist, we believe that the critical differences generated will be useful in routine clinical deci