A 24-hour urine catecholamines test measures the combined levels of adrenaline (epinephrine) and noradrenaline (norepinephrine) produced by the body over a full day. These hormones, released by the adrenal glands during stress or physical activity, regulate crucial functions like heart rate and blood pressure. The test primary screens for rare adrenal neuroendocrine tumors, such as pheochromocytomas or paragangliomas, which hypersecrete catecholamines and cause severe symptoms including persistent high blood pressure, rapid heart rate, sweating, and headaches. Collecting urine over 24 hours provides a reliable baseline, accounting for normal hourly fluctuations throughout the day.