For a 24-hour urine vanillylmandelic acid test to help confirm pheochromocytoma, which instruction should the nurse include?

• A. All urine excreted over the 24-hour period must be saved and refrigerated.
• B. The client may take chlorpromazine during the test.
• C. Only salicylates can be taken for discomfort during the test.
• D. All urine collected over 12 hours is sufficient.

Answer: (A)

Measuring vanillylmandelic acid in a 24-hour urine sample relies on capturing the total daily excretion of catecholamine metabolites. To obtain a true result, every drop of urine during the entire 24-hour period must be saved and kept refrigerated. Completing the full collection accounts for natural fluctuations in hormone production and prevents degradation or bacterial growth that could alter the assay if left at room temperature. This preservation ensures the lab measures the actual amount being excreted over a full day, which is essential for confirming pheochromocytoma.

Medications like chlorpromazine can interfere with catecholamine metabolism and the test result, so taking such drugs during the collection would skew findings. The idea that only salicylates are permissible is not accurate, since many substances can affect VMA levels. And a 12-hour collection is not sufficient because it would miss part of the daily excretion.