Urinary Normetanephrine for the Diagnosis of Canine Pheochromocytoma via Liquid Chromatography-Mass Spectrometry

Pheochromocytomas (PHEO) are rare adrenal medullary tumours characterised by catecholamine secretion. Accurate diagnosis relies on the sensitive measurement of metanephrine (MN) and normetanephrine (NMN); however, the application of liquid chromatography-mass spectrometry (LC-MS/MS) in veterinary medicine remains limited. This study aimed to develop and analytically validate an LC-MS/MS method for the simultaneous quantification of urinary MN and NMN in dogs, establish reference intervals (RIs) for MN- and NMN-to-creatinine ratios (uMN:CR and uNMN:CR), and preliminarily assess the diagnostic utility of uNMN:CR for PHEO detection. The RIs were 2.2-78.9 nmol/mmol for uMN:CR and 4.4-77.4 nmol/mmol for uNMN:CR. Dogs with PHEO showed significantly higher uNMN:CR values compared with dogs with other adrenal masses, non-adrenal disease, or healthy controls. Using the upper RI limit as a threshold, sensitivity and specificity were 91.7% and 35.7%, respectively. Receiver operating characteristic analysis identified an optimal uNMN:CR cut-off of 203.7 nmol/mmol, yielding 78.6% sensitivity, 83.3% specificity, and an overall diagnostic accuracy of 85% (95% CI: 0.68-1.00). These findings support LC-MS/MS as a reliable approach for urinary metanephrine analysis and uNMN:CR as a valuable biochemical tool for PHEO identification in dogs.