Comparison of salivary and serum cortisol levels in mechanically ventilated patients and non-critically ill patients

Background: Although the measuring free cortisol is ideal for assessment of hypothalamicpituitary-adrenal function, it is not routinely measured. Salivary cortisol correlates well with the biologically active free cortisol. Therefore, this study measured the morning basal as well as adrenocorticotropic hormone-stimulated salivary cortisol levels in mechanically ventilated patients and compared the results with non-critically ill patients. Methods: We prospectively enrolled 49 mechanically ventilated patients and 120 patients from the outpatient clinic. Serum and saliva samples were collected between 8 AM and 10 AM. Salivary cortisol levels were measured using an enzyme immunoassay kit. The salivary samples were insufficient in 15 mechanically ventilated patients (30.6%), and these patients were excluded from the final analysis. Results: Mechanically ventilated patients (n=34) were significantly older and had lower body mass index and serum albumin levels and higher serum creatinine levels than non-critically ill patients (n=120). After adjustment for these parameters, both basal and stimulated salivary and serum cortisol levels were higher in mechanically ventilated patients. The increase in cortisol was not significantly different between the two groups. Serum cortisol levels showed a positive correlation with salivary cortisol levels. Among mechanically ventilated patients, both basal serum and salivary cortisol levels were lower in survivors than in non-survivors. Conclusions: Both basal total serum and salivary cortisol levels were elevated in mechanically ventilated patients and in non-survivors.