Final answer:
To diagnose pheochromocytoma, initial testing includes measuring catecholamines and metanephrines in plasma or urine, followed by imaging studies like CT or MRI, and specific radiotracer-based imaging such as MIBG scintigraphy.
Step-by-step explanation:
The diagnosis (Dx) testing modality for pheochromocytoma, which is a tumor of the adrenal medulla that leads to excessive production of catecholamines and resulting hypertension, involves several steps. Initial testing often includes measuring catecholamines and metanephrines in plasma or through a 24-hour urine collection. These tests are highly sensitive and are used to detect the elevated levels of hormones produced by pheochromocytomas. Another method is imaging studies, such as computed tomography (CT) or magnetic resonance imaging (MRI), which can localize the tumor. A radiotracer-based imaging modality called metaiodobenzylguanidine (MIBG) scintigraphy may also be used, as MIBG is taken up by catecholamine-secreting cells, making it particularly useful for locating pheochromocytomas.