Unilateral and bilateral adrenalectomy for pheochromocytoma requires adjustment of urinary and plasma metanephrine reference ranges.

Context: Follow-up after adrenalectomy for pheochromocytoma is recommended because of a recurrence risk. During follow-up, plasma and/or urinary metanephrine (MN) and normetanephrine (NMN) are interpreted using reference ranges obtained in healthy subjects.

Objective: Because adrenalectomy may decrease epinephrine production, we compared MN and NMN concentrations in patients after adrenalectomy to concentrations in a healthy reference population.

Design: A single-center cohort study was performed in pheochromocytoma patients after adrenalectomy between 1980 and 2011.

Subjects: Seventy patients after unilateral and 24 after bilateral adrenalectomy were included.

Main Outcome Measures: Plasma-free and urinary-deconjugated MN and NMN determined at 3 to 6 months and annually until 5 years after adrenalectomy were compared with concentrations in a reference population. Data are presented in median (interquartile range).

Results: Urinary and plasma MN concentrations 3 to 6 months after unilateral adrenalectomy were lower compared with the reference population (39 [31-53] μmol/mol creatinine and 0.14 [0.09-0.18] nmol/L vs 61 [49-74] μmol/mol creatinine and 0.18 [0.13-0.23] nmol/L, respectively, both P < .05). Urinary MN after bilateral adrenalectomy was reduced even further (7 [1-22] μmol/mol creatinine; P < .05). Urinary and plasma NMN were higher after unilateral adrenalectomy (151 [117-189] μmol/mol creatinine and 0.78 [0.59-1.00] nmol/L vs 114 [98-176] μmol/mol creatinine and 0.53 [0.41-0.70] nmol/L; both P < .05). Urinary NMN after bilateral adrenalectomy was higher (177 [106-238] μmol/mol creatinine; P < .05). Changes in urinary and plasma MNs persisted during follow-up.

Conclusion: Concentrations of MN are decreased, whereas NMN concentrations are increased after unilateral and bilateral adrenalectomy. Adjusted reference values for MN and NMN are needed in the postsurgical follow-up of pheochromocytoma patients.