Elecsys cortisol 2

Morning serum cortisol levels were assessed via whole blood sampling (Sarstedt S-Monovette®, Serum Gel with Clotting Activator). Samples were refrigerated at the Jülich Research Centre before analysis in the central laboratory of the University Hospital Cologne, usually on the same day, if not analyzed directly on site in patients whose blood draw was part of their inpatient care at the University Hospital. Samples were analyzed using a commercially available competitive electrochemiluminescence immunoassay (Elecsys® Cortisol II, Roche Diagnostics). The Elecsys® Cortisol II assay makes use of a competition test principle using a monoclonal antibody explicitly directed against cortisol. Endogenous cortisol, liberated from binding proteins with danazol, competes with exogenous cortisol derivatives, labeled with ruthenium complex, for the binding sites on the biotinylated antibody. The measuring range as per the manufacturer’s information is 0.54–633.5 μg/L. All values for healthy seniors in our study fell within the normal range for morning values issued by the manufacturer (5th–95th percentile: 60.1–183.53 μg/L). The monthly inter-assay variation coefficients as assessed by the laboratory as part of their routine quality control measures were between 1.42–4.99% during the time of the study.

Sample collections and salivary cortisol concentration measurements were performed according to a previous study^{16 (link)}. The runners were not allowed to brush their teeth, chew gum, or consume any food or drink except water, 15 min before the sample collection. Saliva samples were collected using Salivette^® cotton swabs (Sarstedt, Nümbrecht, Germany), centrifuged (1,500 × g) at 4 °C for 10 min, then immediately stored at − 80 °C until analysis. ECLIA measurements of salivary cortisol concentrations were performed using the Elecsys Cortisol II on the Cobas 8000 system (Roche Diagnostics K.K, Tokyo, Japan)^{15 (link),16 (link)}. The intra- and inter-assay coefficients of variation for salivary cortisol were 4.1% and 4.6%, respectively. The rate of change in the salivary cortisol concentration by exercise was calculated as the salivary cortisol concentration after exercise divided by the salivary cortisol concentration before exercise (%)^{16 (link)}.

Plasma GDF15 was measured using a commercially available ELISA assay (R&D systems, human: cat no.: SGD150, and mouse: cat no.: DY6385). Intraplate CV was 2.8% and interplate CV was 5.6%. All samples were analyzed in duplicates. Plasma cortisol and growth hormone were measured using an immunological assays, Elecsys Cortisol II (Roche, Basal, Switzerland) and Elecsys hGH (Roche, Basal, Switzerland) automated on a cobas e801. The assay CV were 8% and 6% respectively.