Diagnostic accuracy of post-ACTH challenge salivary cortisol concentrations for identifying horses with equine glandular gastric disease1

Abstract

The aims of this study were to better characterize the adrenal response to i.v. adrenocorticotropic hormone (ACTH) in horses with and without gastric disease and to validate and simplify the ACTH stimulation test by determining the diagnostic accuracy of six consecutive sampling time points after ACTH administration for equine glandular gastric disease (EGGD) and equine squamous gastric disease (ESGD). Twenty-six endurance and eventing horses without clinical disease [Sport Horse Population (SHP)] and an independent population of 62 horses [General Population (GP)] were grouped by gastroscopic findings (no/mild vs. moderate/severe EGGD, grade 0-1 vs. 2-4 ESGD, respectively) and underwent an ACTH stimulation test. Salivary cortisol (ng/mL) was analyzed before and 30, 60, 90, 120, and 150 min after i.v. injection of 1 µg/kg BW synthetic ACTH1-24. The association between having moderate or severe EGGD or ESGD and the amount of salivary cortisol was analyzed by means of receiver-operating characteristic (ROC) analysis. The following explanatory variables were considered: cortisol values for every time point, the area under the curve (AUC)-including all time points and corrected for the baseline-and the partial areas under the curve AUC0-90 and AUC90-150. Sampling after 60 min had highest association with moderate/severe EGGD. The diagnostic potential of the ACTH test was higher for the SHP [sensitivity 100% (95% CI 54% to 100%), specificity 75% (95% CI 51% to 91%), ROC-AUC 91% (95% CI 69% to 98%), 1-sided P-value < 0.001] than for the GP [sensitivity 75% (95% CI 48% to 93%), specificity 52% (95% CI 37% to 67%), ROC-AUC 68% (95% CI 51% to 79%), 1-sided P-value = 0.0064]. There were, however, no significant associations with ESGD. The superiority of sampling after 60 min suggests that the initial release of cortisol rather than its peak or the AUC are relevant regarding EGGD. Even though the wide confidence intervals and thus the lack of diagnostic accuracy do not presently support clinical use, characterization of the adrenal response to an ACTH stimulus improves the understanding of EGGD pathophysiology and its relation to stress.

Effects of breed, management and personality on cortisol reactivity in sport horses

“…Notably, 60 minutes post-stimulation appeared to be the most informative time point, as linear regression models evaluating cortisol concentrations after 90 minutes showed no significant outcome. This is in agreement with our previous study [43], where sampling after 60 minutes also revealed the best association with the occurrence of glandular gastric disease. The present study supports our previous hypothesis [43] that predominantly the initial increase of cortisol after ACTH stimulation is important for the evaluation of the cortisol responsiveness in the context of stress-related disorders.…”

“…For the ACTH stimulation test, based on the estimated weight, a dose of 1 μg/kg BW synthetic ACTH1-24 (Synacthen tetracosactidum 0.25 mg/ml equivalent to 25 IU/mL; Novartis, Vilvoorde, Belgium) was injected intravenously. The dosage was chosen based on previous publications [19, 20, 39, 40]. Saliva samples were taken with salivettes (Sarstedt, Nuembrecht, Germany) before (0 minute – baseline; T0) and 60 (T60) and 90 (T90) minutes after ACTH administration.…”

“…Salivettes were then directly centrifuged at room temperature for 10 min at 185 x g and stored at −20°C until the analysis. For the determination of salivary cortisol concentrations, a competitive enzyme immunoassay (cELISA, Salimetrics, Newmarket, United Kingdom) was used, which has been previously validated for use in horses [19, 20, 40].…”

“…A few studies also reported some associations between equine personality traits and stress parameters [32–34]. Cortisol responses following external stimulation of the HPA axis have been investigated in behavioral studies [23, 35] and for the evaluation of chronic stress in horses suffering from overtraining [36], stereotypies [18] or gastric disease [19, 20].…”

<p>Equine glandular gastric disease: prevalence, impact and management strategies</p>

“…Unfortunately, due to the nonspecific clinical signs associated with EGUS, diagnosis based on clinical signs is unreliable. Blood sucrose and salivary cortisol response to adrenocorticotropin (ACTH) have been evaluated for their diagnostic usefulness in EGGD, but both tests were unreliable 2,3. Endoscopic examination enabling visualization of the lesions in the stomach is the only method to achieve a definitive diagnosis.…”