Why would a doctor order a 24 hour urine for catecholamines test?

To check high levels. Elevated catecholamines in the urine can be associated with hypertension, kidney problems or some excess secretion of catecholamines from other body tissues and creat hypertension and flushing.
Adrenal. This is a test to evaluate for a condition called pheochromocytoma, typically an adrenal tumor that produce too much adrenaline. 24 hr urine is just one of test available to screen for this rare condition.
High blood pressure. This test detects a tumor called a pheochromacytoma. It is very uncommon and usually suspected in pqtients with uncontrolled hypertension.