Efficacy of Single‐voided Urine Metanephrine and Normetanephrine Assay for Diagnosing Pheochromocytoma

Urinary catecholamines (CAs) and their metabolites are usually measured during the process of diagnosing pheochromocytoma (pheo), but a 24‐hour urine collection is not convenient for outpatients. Since 1987 we have utilized “spot” urine metanephrine (MN) and normetanephrine (NMN) assays for management of patients with pheo or adrenal incidentaloma. MN and NMN were measured by radioimmunoassay in 82 patients with surgically proved pheo and 15 patients with incidentaloma. In 10 patients with pheo, MN and NMN were measured with fractional every‐3‐hour urine samples, which were accumulated and then measured as a 24‐hour urinary specimen. Fractions of 3‐hour MN and NMN excretion were constant (MN 98.5 ± 9.6%, NMN 97.6 ± 10.8%; 24‐hour MN and NMN 100%). The average levels of MN and NMN in patients with pheo were 6801 ng/mg creatinine (Cr) (range 93–88,248, median 1426) and 5627 ng/mg Cr (range 219–31,528, mean 3190), whereas the MN and NMN levels in patients with incidentaloma were 123 ng/mg Cr (range 36–246, mean 133) and 251 ng/mg Cr (range 84–472, mean 220), respectively. When we selected a cutoff value for MN + NMN of 1000 ng/mg Cr, the sensitivity was 97.6% and the specificity 100% for diagnosing pheo. When the standard was set as > 500 ng/mg Cr for either MN or NMN, both the sensitivity and specificity were 100%. The assay for MN and NMN is simple and effective, not only for screening but for diagnosing pheo and managing incidentaloma.