How is pheochromocytoma diagnosed?

Patients who are suspected of having a pheochromocytoma should be tested to see if they have too much catecholamines in their system. Catecholamines last only a short time and are quickly broken down by the body into molecules called metanephrines. Metanephrines last much longer and are easier and more accurate to measure than catecholamines. Catecholamines and metanephrines may be measured in the blood or in a 24-hour collection of urine. Depending on the patient's age, family history, and other factors, plasma (i.e. blood) and/or urine tests will be ordered. Levels that are at least twice the upper limit of normal mean that the patient is almost certain to have a pheochromocytoma. For patients with an adrenal incidentaloma, if the metanephrine levels are between 1 and 2 times the upper limit of normal, there is a 30% chance of having a pheochromocytoma. It is important to note that certain medications can interfere with these tests, including some antidepressants and other medications for psychiatric diseases and high blood pressure. In addition, alcohol withdrawal, sleep apnea, and major stress like an operation or significant illness can interfere with test results.