Fryer, Simon M and Dickson, Tabitha and Hillier, Stephen and Stoner, Lee and Scarrott, Carl and Draper, Nick (2014). A Comparison of Capillary, Venous, and Salivary Cortisol Sampling

Venipuncture is expensive, invasive and impractical for many sport science and clinical based settings. Salivary free cortisol is often cited as a non-invasive practical alternative. However, when cortisol concentrations exceed the corticosteroid binding globulin (CBG) point of 500nmol·L a lack of agreement between salivary and venous blood cortisol have been found. Alternatively, capillary blood may present a minimally invasive, cost effective and practical surrogate for determining cortisol concentration. Purpose: The aim of this study was to determine whether cortisol concentrations sampled from (a) capillary blood and (b) saliva accurately reflect those found in venous blood across a large range of concentrations following intense exercise. Methods: Eleven healthy aerobically trained male subjects were recruited. Capillary, salivary and venous blood samples were collected pre and post (immediately post and post 5, 10, 15 and 20 minutes) a treadmill V O2 max test. Total and free cortisol samples were analysed via an ELISA method using monoclonal antibodies. Results: Capillary and venous concentrations increased at a similar rate following exercise (Cohen’s d between 0.14 – 0.33), increasing up to 15 minutes post before a decline was seen. Salivary cortisol values increased at a slower rate compared to venous and capillary cortisol, but continued to increase post 15 minutes (Cohen’s d 0.19 – 0.47 and 0.09 – 0.72 respectively). Conclusions: Capillary and not salivary cortisol accurately reflects concentrations assayed from venous blood across a range of values below and above the CBG binding point. Capillary sampling provides a minimally invasive, cost effective practical surrogate for assessment of HPA function. Introduction Cortisol is the primary stress hormone used to assess function of the hypothalamic-pituitaryglad (HPA) axis, and is present in the body as both free and bound forms. Cortisol is dispersed through all water spaces within the body, and can be sampled from urine, serum and saliva. However, each technique can often be constrained by situational (sampling method) or analytical problems. Urinary analysis often fails to assess rapid changes in concentrations over time; salivary analysis represents only the biologically active free fraction of cortisol (cortisol which is not bound to the corticosteroid binding globulin (CBG),