Comparison of results of adrenocorticotropic hormone stimulation and low-dose dexamethasone suppression tests with necropsy findings in dogs: 81 cases (1985-1995).

OBJECTIVE: Comparison of diagnostic accuracy of results of low-dose dexamethasone suppression (LDDS) and ACTH stimulation tests with necropsy findings in 81 dogs.

DESIGN: Retrospective study.

ANIMALS: 81 dogs that had undergone screening tests for hyperadrenocorticism and that had a complete necropsy report.

PROCEDURE: Medical records were evaluated for results of CBC, serum biochemical analysis, urinalysis, endocrine testing, signalment, treatment, and necropsy findings. Each dog was definitively classified as having true-positive, true-negative, false-positive, or false-negative results. Statistical analyses included determination of prevalence, apparent prevalence, accuracy, number of dogs misclassified, sensitivity, specificity, and positive- and negative-predictive values.

RESULTS: Of the 81 dogs that fit the criteria for selection, 40 (49%) were confirmed as having hyperadrenocorticism (30 had pituitary-dependent disease and 10 had adrenal gland tumors). Forty-one dogs had illnesses attributable to a cause other than disease of the adrenal glands. Sensitivity of ACTH stimulation and LDDS tests were 95 and 96%, respectively. Specificity for the ACTH stimulation test was higher (91%) than that of the LDDS test (70%). When prevalence of the disease in the study population was taken into consideration, the positive-predictive value for the ACTH stimulation test was 91%, compared with 76% for the LDDS test.

CLINICAL IMPLICATIONS: The ACTH stimulation test was more specific than the LDDS test, although sensitivity was similar for both tests. The ACTH stimulation test also had a significantly higher positive-predictive value than the LDDS test when a prevalence of 25% was taken into consideration.