Diagnostic efficacy of plasma ACTH-measurement by a chemiluminometric assay in canine hyperadrenocorticism

This retrospective study was performed to investigate the diagnostic efficacy of the chemiluminometric ACTH-measurement to differentiate between pituitary and adrenal dependent hyperadrenocorticism (HAG) in dogs. 49 dogs with pituitary HAG, 10 dogs with adrenal HAG and 1 dog with a combination of both pathologies were included. Dogs with HAG like symptoms, where HAG had been ruled out, served as controls (n = 18). All dogs with adrenal HAG, as well as 9 dogs with pituitary HAG had an ACTH concentration below the detection limit of 2.2 pmol/l (10 pg/dl) plasma. Using 2.2 pmol/l as a cut-off the sensitivity and specificity to diagnose pituitary HAG was 0.82 (95% CI 0.686-0.914) and 1 (95 % CI 0.692-1), respectively. With the help of the chemiluminometric assay, a correct classification was possible in 85% of patients with HAG. As an ACTH-concentration below the detection limit was found in dogs with adrenal as well as pituitary HAG, additional discriminatory tests are necessary in these cases.