Evaluation of the Cortisol‐to‐ACTHRatio in Dogs with Hypoadrenocorticism, Dogs with Diseases Mimicking Hypoadrenocorticism and in Healthy Dogs

Abstract

BackgroundThe adrenocorticotropic hormone (ACTH) stimulation test is the gold standard for diagnosing hypoadrenocorticism (HA) in dogs. However, problems with the availability of synthetic ACTH (tetracosactrin/cosyntropin) and increased costs have prompted the need for alternative methods.ObjectivesTo prospectively evaluate the cortisol‐to‐ACTH ratio (CAR) as a screening test for diagnosing canine HA.AnimalsTwenty three dogs with newly diagnosed HA; 79 dogs with diseases mimicking HA; 30 healthy dogs.MethodsPlasma ACTH and baseline cortisol concentrations were measured before IV administration of 5 μg/kg ACTH in all dogs. CAR was calculated and the diagnostic performance of ACTH, baseline cortisol, CAR and sodium‐to‐potassium ratios (SPRs) was assessed based on receiver operating characteristics (ROC) curves calculating the area under the ROC curve.ResultsThe CAR was significantly lower in dogs with HA compared to that in healthy dogs and in those with diseases mimicking HA (P < .0001). There was an overlap between HA dogs and those with HA mimicking diseases, but CAR still was the best parameter for diagnosing HA (ROC AUC 0.998), followed by the ACTH concentration (ROC AUC 0.97), baseline cortisol concentration (ROC AUC 0.96), and SPR (ROC AUC 0.86). With a CAR of >0.01 the diagnostic sensitivity and specificity were 100% and 99%, respectively.Conclusion and Clinical ImportanceCalculation of the CAR is a useful screening test for diagnosing primary HA. As a consequence of the observed overlap between the groups, however, misdiagnosis cannot be completely excluded. Moreover, additional studies are needed to evaluate the diagnostic reliability of CAR in more dogs with secondary HA.

ACTH Level and Sodium-Potassium Ratio in Screening of Primary Canine Hypoadrenocorticism

“…The absence of negative feedback results in a high serum level of ACTH [6]. The owner's complaints are related to nonspecifi c signs, as vomiting, lethargy, weakness and anorexia that are associated to multiple systems and illnesses, as gastrointestinal, renal or neurologic disorders.…”

“…The ACTH stimulation test is the gold standard for diagnosing HA in dogs and consists to measure cortisol levels before and after administration of synthetic or commercial gel preparations of purifi ed porcine pituitary extract [6,7].…”

“…However, problems with the availability of synthetic ACTH and increased costs have prompted the need for alternative methods, especially in developing countries [6].…”

“…Electrolytes abnormalities may be used to distinguish primary to secondary HA, as they hardly change in secondary HA [2,3]. Therefore, calculation of the sodiumpotassium ratio and plasma ACTH level is a useful screening test for diagnosing primary HA [6]. The Na: K was decreased (23:1), so the suspicion of diagnosis was HA, confi rmed by the high plasma ACTH level (248 pg/ mL).…”

Altered Serum Thyrotropin Concentrations in Dogs with Primary Hypoadrenocorticism before and during Treatment

“…1,2 Due to the lack of the negative feedback on the pituitary gland, an increase in plasma concentrations of endogenous ACTH is typically observed. [3][4][5] Human patients with primary HA can have thyroidstimulating hormone (TSH; thyrotropin) concentrations that are increased despite normal T4 concentrations before initiating glucocorticoid treatment. 6 As TSH will normalize after glucocorticoid supplementation, the increase has been explained by a lack of the inhibitory effect of cortisol on the secretion of TSH.…”