Comparison of the determination of cortisol in canine saliva by chemiluminescence immunoassay and liquid chromatography–tandem mass spectrometry

We determined saliva cortisol concentrations (SCCs) in samples from 36 dogs using a chemiluminescence immunoassay (CLIA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) before and after a 10-min veterinary visit. The median cortisol concentration of the 77 samples analyzed with CLIA was 1.34 nmol/L, and the concentration of samples analyzed with LC-MS/MS was 1.30 nmol/L. With an intercept (a) of -0.06 (95% CI: -0.16 to 0.02) and a slope (b) of 0.97 (95% CI: 0.90-0.97) the Passing-Bablok regression revealed that there were no significant systematic and proportional differences between the 2 methods. In the Bland-Altman analysis, the bias was 0.08 nmol/L (95% CI: -0.38 to 0.54 nmol/L) between the 2 methods. Comparing the hormone levels in the saliva of 36 dogs before and after a veterinary visit, the CLIA method had a mean difference of 0.03 nmol/L (95% CI: -1.72 to 4.75 nmol/L; <i>p</i> = 0.35) and the LC-MS/MS method a mean difference of 0.12 nmol/L (95% CI 95%: -2.43 to 4.40 nmol/L; <i>p</i> = 0.62). Comparison of cortisol changes before (<i>p</i> = 0.86) and after (<i>p =</i> 0.79) the veterinary visit revealed no differences in using either the CLIA or LC-MS/MS methods. There was also no difference in the assessment of hormone increase or decrease between CLIA (<i>p</i> = 0.72) and LC-MS/MS (<i>p</i> = 0.17). Overall, the measurement of SCC in dogs by either CLIA or LC-MS/MS provided comparable results.