For a client undergoing a 24-hour urine test for pheochromocytoma, when should the nurse start collecting urine?

The correct process for starting the collection of urine during a 24-hour urine test for pheochromocytoma is to begin after discarding the first voiding. This procedure is important because the first voided urine is not representative of the total urine output over the 24-hour period. It may contain metabolites from previous hours and not reflect the changes in hormone levels or metabolites related to pheochromocytoma that are assessed during the test.

By discarding the first void, the nurse ensures that the collected urine reflects the physiological status of the client during the entirety of the 24 hours, starting from the second void onward. This helps in obtaining accurate levels of catecholamines and their metabolites, which are essential in diagnosing pheochromocytoma. Starting the collection at this point enhances the reliability of the test results, making it easier to confirm or rule out this condition.