How the low-dose dexamethasone test helps diagnose dog Cushing's

Abstract

BACKGROUND: The low-dose dexamethasone suppression test (LDDT) is considered an accurate screening and valuable differentiation test in dogs with suspected hyperadrenocorticism (HAC). A recent study showed that the different response patterns not only provide complementary information about etiology, but also the probability of HAC in these patients. OBJECTIVES: We aimed to determine the diagnostic test performance of LDDT response patterns in a population of dogs from an animal hospital. METHODS: The electronic database was retrospectively searched for dogs suspected of HAC that were given an LDDT. Dogs with acute non-adrenal illnesses during the test were excluded. Response patterns were classified as complete suppression, lack of suppression, partial suppression, escape, inverse, and increasing patterns. Cortisol concentrations ≥ 27.59 nmol/L (≥1 µg/dL) 8 hours after dexamethasone administration were considered positive results irrespective of the patterns observed. Calculations included likelihood ratios (LRs) and predictive values (PVs). RESULTS: HAC and non-adrenal illness were diagnosed in 115 (54%) and 62 (46%) dogs, respectively. The positive (+) LRs (95% CI) for the lack of suppression, partial suppression, escape, and an inverse pattern to diagnose HAC were infinite, 8.09 (2-32.72), 3.23 (0.75-14), and 0.2 (0.06-0.73), respectively. CONCLUSIONS: The study confirms that the "lack of suppression" pattern strongly supports a diagnosis of HAC. It shows that the "partial suppression" pattern moderately increases, and the "inverse" pattern decreases the likelihood of HAC. The fact that the study found no association between the "escape" pattern and a diagnosis of HAC, does not support its integration into decision making.