Biological uniqueness and the definition of normality. Part 2--The endocrine 'fingerprint' of healthy adults

Abstract

In an accompanying paper, we discussed the relevance of biological uniqueness for research in physiology and medicine. We proposed the concepts of subject-specific homeostasis, or 'intrinsic' homeostasis. Here, we illustrate this concept with the example of the endocrine 'fingerprint'. 9 hormones were measured in the blood of 8 normal subjects during 2 consecutive mornings, under a standardised resting condition. The concentrations of the hormones were subject-specific. They varied up to 6-fold between subjects, but were stable from one day to the next for each individual. TSH and FSH showed the wider inter-individual range of values, together with a very high level of day-to-day stability (r = 0.99 in both cases). In contrast, the inter-individual range of cortisol concentration was the smallest (1.5-fold) and the day-to-day stability of cortisol concentrations within each subject was low. A total of 21 non-hormonal variables were also measured. They varied less than hormones between subjects, but, with the exception of the electrolytes, most showed stability over the 2 days of sampling. We conclude that the organisation of hormonal and non-hormonal homeostasis varies between subjects to a greater extent than generally acknowledged and suggest that these differences express subject-specific constraints in the organization of homeostasis.