5th April 2024

Diagnosis

There is no definitive test for phaeochromocytomas but the initial approach in a patient with symptoms suggestive of it should be to measure catecholamine levels. This can be done through a blood test but catecholamine levels in the blood can be raised for a variety of reasons e.g., stress, and aren’t very specific for pheochromocytomas. Testing 24-hour urine collections for catecholamine levels is a much more specific test.

In a minority of patients, plasma or urine catecholamine levels may yield false-positive results. This may be because catecholamine levels in these individuals are always raised e.g., poor renal excretory function. In this cohort of patients, a clonidine suppression test can be used. Clonidine acts on adrenoreceptors at nerve terminals to decrease adrenaline release. However, a phaeochromocytoma will release adrenaline independently of this system and so adrenaline levels remain raised despite the administration of clonidine.

If there is biochemical evidence of a phaeochromocytoma, or if suspicion remains high despite negative tests, imaging such as CT or MRI of the adrenal glands are needed to confirm the diagnosis.