Urinary free metanephrines and suitability of available quality control material

摘要

I read with interest the recent publication by Peitzsch et al. [1], who evaluated liquid chromatography tandem mass spectrometry (LC-MS/MS) for the measurement of free and deconjugated urine metanephrines for the biochemical assessment of phaeochromocytoma (PCC). Data presented clearly demonstrated the potential benefits of measuring free urine metanephrines instead or in addition to deconjugated urine metanephrines (UMets). Specifically data showed that median free normetanephrine concentrations were ten-fold higher in patients with PCC compared to median concentrations observed in the control group. No differences were observed between free and deconjugated metanephrine levels. A similar publication by Pamporaki et al. [2] confirmed that plasma free normetanephrine levels, not metanephrine are superior to deconjugated plasma normetanephrine for the diagnosis of PCC. Data from this study showed that median concentrations of free normetanephrine were 17-fold higher in patients with PCC than in the reference population, a 72% larger difference than that for the 10-fold higher median concentrations of plasma deconjugated normetanephrine.