Use of salivary cortisol and cortisone in the high and low dose synacthen test

CONTEXT: Salivary cortisone reflects serum cortisol levels, is more sensitive than salivary cortisol at lower values of serum cortisol and is non-invasive. OBJECTIVE: To investigate the relationship between serum cortisol and salivary cortisol and cortisone following low and high-dose synacthen. DESIGN AND SETTING: Prospective pharmacodynamic studies in clinical research facilities. PARTICIPANTS AND INTERVENTION: 35 dexamethasone-suppressed, healthy adult males underwent an intravenous synacthen test: N=23 low-dose (1mcg), N=12 high-dose (250mcg). Paired serum and salivary samples were taken at 15 sampling points over 120 minutes. MAIN OUTCOME MEASURE: Serum cortisol and salivary cortisol and cortisone were analyzed for correlations and by a mixed effects model. RESULTS: At baseline the correlation between serum cortisol and salivary cortisol was weak with many samples undetectable (r=0.45, NS), but there was a strong correlation with salivary cortisone (r=0.94, p<0.001). Up to 50 minutes following synacthen the correlation coefficient between serum cortisol and salivary cortisol and cortisone was <0.8, but both had a stronger correlation at 60 minutes (salivary cortisol r=0.89, p<0.001, salivary cortisone r=0.85, p<0.001). The relationship was examined excluding samples in the dynamic phase (baseline to 60 minutes). Salivary cortisol and cortisone showed a close relationship to serum cortisol. Salivary cortisone showing the stronger correlation: Salivary cortisol r=0.82, p<0.001, salivary cortisone r=0.96, p<0.001. CONCLUSION: Following synacthen, both salivary cortisol and cortisone reflect serum cortisol levels but there is a lag in their rise up to 60mins. The results support further research for possible future use of a 60min salivary cortisone measurement during the synacthen test.