Evaluation of canine ACTH stimulation test with direct enzyme immunoassay for serum cortisol in Taiwan

Abstract

In this study, we evaluated cortisol concentrations from 53 healthy dogs in response to ACTH stimulation test. The concentrations of serum cortisol were directly determined by a competitive enzyme immunoassay (EIA) with a 104‐fold diluted self‐made monoclonal antibody. The sensitivity of EIA was 0.1 ng mL−1 with intra‐assay and interassay coefficients of variation of 8.28 ± 0.09 and 14.60 ± 0.28%, respectively. The recovery rates for 1, 5 and 10 ng mL−1 of cortisol in dog serum were 77.8–128.7% with direct detection. The parallelism test revealed its reliability to detect directly the cortisol concentration in canine serum without extraction. In general, this EIA showed low crossreactivities with a variety of steroids. In the ACTH stimulation tests, we gave each dog 250 µg ACTH (Cortrosyn® Organon) intramuscularly and collected blood samples before and 1 h after administration of ACTH. The cortisol concentrations from 53 healthy dogs were 0.85–14.63 ng mL−1 pre‐ and 3.06–37.22 ng mL−1 post‐test, respectively. Sex and age did not significantly affect the cortisol concentrations in response to ACTH stimulation, but the large breeds (body weight > 25 kg; most of them were German shepherd dogs) showed lower cortisol responses than the smaller breeds. Thus, the results of this test suggested that body weight and breed might play an important role in adrenal dynamic tests.