Duration of blood plasma cortisol suppression after a low-dose dexamethasone suppression test in dogs

Abstract

The aim of this study was to determine the duration of the suppressive effect on the hypothalamus–pituitary–adrenocortical axis as measured by plasma cortisol concentration after injection of a low dosage of dexamethasone (0.01 mg/kg BW) used within the low-dose dexamethasone suppression test (LDDST). A LDDST was performed on ten clinically healthy dogs with unremarkable haematological and plasma biochemical profiles, abdominal X-ray, abdominal ultrasonography and fine needle aspiration cytology of the liver. Two of them were excluded from the analysis. Blood samples were collected at baseline, 4 and 8 h (standard protocol of a LDDST) and, additionally, at 24, 48, 72 and 96 h after the application of dexamethasone. Plasma cortisol concentrations 10 ng/ml. The median 4, 8 and 24 h plasma cortisol concentrations were significantly lower than the median baseline plasma cortisol concentration, whereas at the remaining times no significant changes were seen compared to the median baseline value. The suppression of plasma cortisol induced by dexamethasone in a dosage of 0.01 mg/kg BW can last at least 48 h in individual dogs. Therefore, a repeated LDDST should be performed at the earliest 3 days after the prior test to prevent artificial results.