Does the Cortisol:CRP ratio inform the measurement of Individual Burden of Illness for Depression in Community Samples?

Abstract Objective To test if the collection of an objective biological index of the balance between two major physiological systems significantly adds to the contribution made by an IBI-D. Methods Responses to scales measuring depressive symptoms, functional impairment due to mental and physical health, and saliva samples were collected from 111 community volunteers from rural Australia. Saliva was assayed for cortisol and C-Reactive Protein concentrations, and the ratio of these was used as an indicator of the balance between the Hypothalamic-Pituitary-Adrenal axis and the inflammatory response from the immune system. Results Principal Components Analysis (PCA) produced two- and three-factor solutions from the psychological and biological data, and were used to form weighted models of two IBI-D equations. Stepwise regression analysis indicated that the addition of the biological index to the second IBI-D made a significant extra contribution to variance in depression score. Discussion Valid assessment of the symptoms of depression provides one aspect of diagnostic information, but the addition of biological information can further inform clinicians and researchers about the effect that these symptoms have upon patient functioning.