Evaluation of urine free and fractionated catecholamine metabolites in the diagnosis of pheochromocytoma

Objective The diagnostic values of urine free and fractionated catecholamine metabolites (including metanephrine MN and normetanephrine NMN, usually known as MNs) were established and their clinical value was evaluated. Methods Using high performance liquid chromatography tandem mass spectrometry(HPLC-MS/MS), urine free MNs (f-MN, f-NMN) and fractionated MNs(t-MN, t-NMN) from 180 cases of non-pheochromocytoma and 54 cases of pheochromocytoma (PCC)patients were detected respectively.Receiver operating characteristic curve (ROC) was used to establish clinical reference cut-off value for different forms of MNs, and diagnostic efficacy of free, fractionated and total MNs was evaluated. Results (1) The cut-off values of f-MN, f-NMN, t-MN and t-NMN were 47.8 μg/24 h, 52.3 μg/24 h, 224.9 μg/24 h and 664 μg/24 h, respectively. The cut-off values of total f-MNs and total t-MNs were 126 μg/24 h and 1 070 μg/24 h, respectively. (2) The correlation between f-MN and t-MN (r=0.976, P 0.05). There was no significant difference in sensitivity (90.74% vs 92.59%, P>0.05), specificity (99.44% vs 96.67%, P>0.05) and AUC (0.944 vs 0.959, P>0.05) between f-NMN and t-NMN. The combined diagnostic value of MN and NMN (total MNs) was higher than MN (free type:0.932>0.579, fractionation type: 0.960>0.730), which was similar to NMN. Conclusions The diagnostic performance of urine free NMN or total MNs for PCC is similar to that of fractionated typewhich can meet the clinical needs.With few influencing factors, free type MNs may be used as an alternative indicator for PCC screening in the future. Key words: Pheochromocytoma; Catecholamines; Chromatography, high pressure liquid; Tandem mass spectrometry; Laboratory critical values; Urinalysis