Diagnosis of pheochromocytoma. Reflections on a controversy.

The optimal evaluation of patients suspected of having a pheochromocytoma remains controversial. The availability of large numbers of hormone assays and the need to exclude with certainty a potentially lethal disorder with an unpredictable course have led to various approaches to biochemical testing. The quantification of the urinary excretion rate of catecholamine and catecholamine metabolites has been the mainstay of the diagnosis of pheochromocytoma. The most useful urine tests are those that measure concentrations of metanephrines (normetanephrine and metanephrine combined), vanillylmandelic acid (VMA), and free (unconjugated) catecholamines. The 24-hour urine collection is the standard. Nighttime urine collections, 4to 8-hour urine or single voided urine collections, and random 1-hour urine specimens have been recommended. Each test varies in sensitivity and specificity, with urinary metanephrines having the best sensitivity and specificity. All are susceptible to chemical interference from drugs, with the measurement of metanephrines being least affected. Thus, assays of urinary metanephrines are adequate to diagnose pheochromocytoma in most patients. This test is readily available and relatively inexpensive.