Optimized Reference Intervals for Plasma Free Metanephrines in Patients With CKD

To the Editor: The diagnostic work-up of pheochromocytoma/paraganglioma (PPGL) among patients with chronic kidney disease (CKD) is a clinical challenge. Impaired renal elimination of catecholamines and their metabolites confounds urinary tests, while increased plasma concentrations of free metanephrines in patients with CKD also complicate interpretation of plasma tests.1, 2, 3 We therefore aimed to establish optimal reference intervals for plasma free metanephrines and 3-methoxytyramine in patients with CKD stages 3 and 4 or receiving hemodialysis (HD). This prospective multicenter study included 234 patients (79 CKD3, 48 CKD4, and 107 receiving HD) and an aged-matched reference population of 173 individuals (Table 1; Item S1). Measurements of plasma free normetanephrine, metanephrine, and 3-methoxytyramine were performed using liquid chromatography–tandem mass spectrometry (LC-MS/MS).4