Disappearance rate of catecholamines, total metanephrines, and neuropeptide Y from the plasma of patients after resection of pheochromocytoma

Background: Plasma free metanephrines are a more reliable analyte to measur e than catecholamines for the biochemical diagnosis of pheochromocytomas. W e hypothesized that the long persistence of total (sulfate-conjugated plus free) metanephrines in the blood might have a significant diagnostic value. Methods: We measured plasma concentrations of catecholamines and total meta nephrines (sulfate-conjugated plus free forms) by HPLC with amperometric de tection, and neuropeptide Y (NPY) by an amplified ELISA in seven patients b efore and after removal of their pheochromocytomas. The results for catecho lamine, total metanephrines, and NPY in each patient were analyzed for up t o 120 min, starting from the time of tumor vessel clamping. The persistence of analytes was quantified as the area under the concentration-time curve over 120 min. Results: On the basis of the upper reference limit for each variable, plasm a free norepinephrine (NE) and epinephrine (E) concentrations were increase d preoperatively in at least one sample in seven and six patients, respecti vely. Total normetanephrine (NMN) and metanephrine (MN) were increased in a ll samples in seven and six patients, respectively. NPY was increased 2- to 465-fold. After removal of the tumor, MN and NMN showed a higher average r elative increase above the upper limit of the reference interval than NE an d E (P = 0.05), whereas NPY was intermediate. The persistence of increased values was significantly shorter for catecholamines than for metanephrines. The half-life estimated by nonlinear regression was 12.3 +/- 7.8 min for N PY. Significant correlations were observed among NE, E, NMN, MN, and NPY co ncentrations, but parent markers (E and MN or NE and NMN) did not appear si gnificantly intercorrelated. Conclusions: A larger increase and a longer persistence of total metanephri nes (reflecting predominantly sulfoconjugated metanephrines) than catechola mines and NPY in plasma may contribute to their greater diagnostic accuracy in pheochromocytoma. (C) 2001 American Association for Clinical Chemistry.