Biological uniqueness and the definition of normality. Part 1--The concept of 'intrinsic' homeostasis

Abstract

The patterns of biochemical and physiological variables values are subject-specific and quite stable over time. Thus, within the limits imposed by physiological requirements, the composition of the 'milieu intérieur' varies between individuals. It follows that having all values of blood constituents within the norm (defined statistically from populations of healthy subjects) might not be sufficient to identify biological normality, and a revised definition of biological normality should take into account inter-individual differences. Our concept of 'intrinsic' homeostasis means that the differences between subjects' concentrations of blood constituents express subject-specific constraints in the organization of their physiology, and that these differences might play a greater role than usually recognized. We list the consequences for medical research of the existence of biological uniqueness and propose to give more importance to the study of biological 'fingerprints' and 'intrinsic' homeostasis in physiology and clinical medicine.