Determination of catecholamines and their O-methyl metabolites, normetanephrine (NMN) and metanephrine (MN), in biological fluids plays an important role in the diagnosis of pheochromocytoma (PHEO) ? chromaffin cells tumor. The aim of the study was to validate a HPLCED (Electrochemical Detection) method for the determination of MN and NMN in blood plasma and to compare the obtained data with those published previously. The ability of the proposed method to distinguish the patients with and without PHEO has been proved and the results were compared with the HPLC determination of free catecholamines in urine. Both methods interpret the results in relation to the presence of PHEO. Finally the concentration limits for patients with and without PHEO have been established. Analytical parameters of the method including the repeatability, accuracy, LOD, LOQ and reproducibility as well as its sensitivity and specificity in tumor diagnosis were determined. The hypertonic patients should be included in patients without PHEO as they increase the concentration limit. This helps to avoid false positive results.
