Biological variation of baseline serum cortisol concentration in healthy dogs, part 2: clinical applications

Biological variation tools can be used to quantify uncertainty inherent in laboratory measurements and assist veterinarians in clinical decision making.

Biological variation tools for interpretation of baseline cortisol concentrations in dogs are calculated using data obtained during part 1 of this study.

Expanded measurement uncertainty and bidirectional dispersion with 95% probability for baseline cortisol are 13.7 and 64.9% respectively, and these values can be used to establish a "grey-zone" around a population-based reference interval limit to guide clinical investigations. Index of individuality is intermediate (1.14), and forty-two samples would be needed to estimate an individual dog's homeostatic setpoint for cortisol. These values support current recommendations to interpret baseline cortisol concentrations in a broader clinical context utilizing ancillary testing when appropriate. The unidirectional reference change value for baseline cortisol is 77.3% with 95% probability, which can be helpful in determining the significance of changes in serial measurements.

Biological variation tools help define uncertainty around measurement of baseline cortisol concentrations in dogs, encourage an individualized approach to spectrum-of-care, and reinforce current consensus statements that rely on clinical signs combined with dynamic testing for the diagnosis of hyper- or hypoadrenocorticism rather than baseline cortisol concentrations alone.