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

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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 misclassifled, sensitivity, specificity, and posltive-and negative-predictive values. Results— Of the 81 dogs that fit the criteria for selection, 40 (49%) were confirmed as having hyperadreno-corticism (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. (J Am Vet Med Assoc 1997;211:322–325)