OBJECTIVE: To evaluate the specificity/sensitivity and predictive values of urine spot metanephrines-to-creatinine ratios to diagnose canine pheochromocytomas and to determine whether there is a correlation between urine catecholamine levels and tumor volume. METHODS: In a retrospective study, 32 client-owned dogs with adrenal tumors were identified (13 nonpheochromocytoma and 19 pheochromocytoma). Medical records were evaluated for patients undergoing adrenalectomy between August 2020 and August 2023. Patients were divided into groupings of pheochromocytoma and other adrenal tumor diagnosis on the basis of histopathology. RESULTS: Urine spot normetanephrine concentrations were significantly elevated in dogs with pheochromocytomas compared to dogs with other adrenal tumors. Sensitivity was 78.9%, specificity 76.9%, positive predictive value 83.3%, and negative predictive value 71.4% for discriminating between pheochromocytoma and nonpheochromocytoma. Spot urine metanephrine concentrations were not significantly different between the 2 groups. Only 5 of 19 pheochromocytoma patients had urine normetanephrine concentrations >
4 times the upper reference limit, which is the previously established diagnostic cutoff. Median tumor volume did not correlate with normetanephrine values, nor did those values correlate to patients that experienced intraoperative complications. Twenty-one percent of cases were biochemically silent pheochromocytomas. CONCLUSIONS: Urine normetanephrine-to-creatinine levels but not metanephrine-to-creatinine levels can potentially differentiate a pheochromocytoma from a nonpheochromocytoma. CLINICAL RELEVANCE: Previously published guidelines of 4 times the upper reference limit in spot urine metanephrines testing used to diagnose pheochromocytomas will lead to a significant number of missed diagnoses.