What if the results are negative in the 24 hour catecholamine urine test?  

R/O adrenal tumor. Catecholamines are typically produced by functioing adrenal tumors causing elevated blood pressure and rapid pulse. This can be ruled out with a normal 24 hour test.
Pheochromocytoma. A negative 24 hour catecholamine test would make it very unlikely that you have a pheochromocytoma (a rare, catecholamine-secreting tumor usually benign and arising from the adrenal gland that may precipitate life-threatening hypertension).

Related Questions

What are the other causes of elevated catecholamines in a 24 hour urine test if it is not a pheochromocytoma?

How High? There are many causes of elevated catechols in a 24 hour urine sample. Depending on the test used medications can interfere with catechol levels, including things as simple as acetaminophen & certain beta blocker medications. If only mildly elevated something as simple as stress can elev the labs. There is a cond called a paraganglioma. The cond's make diff catechols, the breakdown is helpful. Read more...