Background Pheochromocytoma (PCC) is rare in cats and plasma (PL) and urinary (U) metanephrines (metanephrine [MN]; normetanephrine [NMN]) measurement is rarely described in cats. Objectives We evaluated the utility of PL and U MNs measurement in 10 healthy cats and a cat with a confirmed diagnosis of pheochromocytoma (PheoCat), using liquid chromatography with tandem mass spectrometry (LC‐MS‐MS). Methods Urine and EDTA PL samples collected from each of the 10 cats and the PheoCat were promptly stored at −80°C and remained frozen until analysis. To evaluate U MNs stability, an additional urine sample collected from the healthy cats was refrigerated for 24 hours before freezing. Urinary creatinine concentration (Creat) was assessed using the same spot urine samples to calculate U MNs‐to‐creatinine ratios. Results The PL‐MN and PL‐NMN median concentrations of the healthy cats were 2.73 and 7.02 nmol/L, respectively. The median U‐MN/Creat and U‐NMN/Creat ratios were 70 and 139 μg/g, respectively. The PheoCat had a PL‐MN of 3.68 nmol/L, PL‐NMN of 66.27 nmol/L, U‐MN/Creat of 179 μg/g, and U‐NMN/Creat of 1262 μg/g. The PheoCat had markedly increased concentrations of both PL and U MNs when compared to the healthy cats. No significant difference was found between U MNs measured in urine samples that underwent 24 hours of refrigeration in comparison to those that were frozen immediately. Conclusions We report preliminary reference intervals for PL and U MNs in cats using LC‐MS‐MS and the potential clinical applicability of these biomarkers for the diagnosis of PCC in cats.

Pheochromocytoma in cats is a rare clinical condition characterised by the development of a secretory endocrine tumour that arises from the adrenal medulla. An 8‐year‐old castrated male, domestic shorthair cat was referred for further investigation of a 4‐month history of progressive weight loss with normal appetite, polyuria/polydipsia, generalised weakness, and severe hypertension. Sonography and computed tomography of the abdomen disclosed a mass arising from the left adrenal gland. The contralateral adrenal gland was normal in size and shape. Results from a low dose dexamethasone suppression test and measurements of plasma aldosterone concentration and plasma renin activity ruled out a cortisol‐secreting tumour and aldosteronoma. The clinical presentation made a sex‐steroid secreting tumour unlikely. Increased plasma metanephrine and normetanephrine concentrations prioritised the differential diagnosis of pheochromocytoma. The cat underwent adrenalectomy of the left gland and histopathological diagnosis with immunohistochemical markers confirmed the diagnosis.