(EN07) Endogenous ACTH as an Aid for Primary Hypoadrenocorticism Diagnosis After Glucocorticoid Treatment Beginning

Abstract: Background – ACTH stimulation test (ACTHST) is the gold standard for primary hypoadrenocorticism (PHA) diagnosis. Cortisol/ACTH ratio can be applied alternatively due the high endogenous ACTH (eACTH) levels in those cases. Adrenal crisis severity and eventual difficulties with synthetic ACTH availability and eACTH measurement may lead to the beginning of glucocorticoid therapy (GCT) in suspect cases before PHA confirmation, impairing the interpretation of confirmatory tests. Hypothesis/Objectives – Dogs with PHA don´t suppress eACTH within reference range (5-45 pg/mL) after GCT. Increased eACTH levels in dogs on GCT argues in favor of PHA diagnosis in suspected cases. Animals – Twenty-three dogs with previous confirmed PHA by the ACTHST and twelve controls submitted to GCT. Methods – Cross-sectional study of dogs with PHA to measure plasma eACTH (Immulite, Siemens), and prospective comparison of eACTH before (T0) and after 5-10 days (T1) on GCT in the controls. Samples from the PHA group and control dogs in T1 were collected at least 18 hours after the last GC administration. Clinical signs, hematological, and serum biochemistry analysis were also compared. Results are expressed as median and range. Results – Median eACTH (485; 21.5-1250 pg/mL) from PHA dogs was higher (P< 0.0001) than controls in T1 (9.63; 1-34.4 pg/mL). The GCT significantly decreased eACTH from T0 (20.3; 1-142 pg/mL, P=0.0488). The PHA dogs were receiving less (P< 0.0001) prednisone (0.075; 0-1.78 mg/kg/q24h) than controls (0.5; 0.35-1.29 mg/kg/q24h). Conclusions and Clinical Importance – Low-dose GCT doesn´t normalize eACTH in PHA, a finding that may aid confirming this suspicion in dogs already on GCT.