True or false: When produced, free catecholamines (NE and EPI) are short-lived. They are best measured in the urine, though catecholamine metabolites are best measured in the serum.

True or false: When produced, free catecholamines (NE and EPI) are short-lived. They are best measured in the urine, though catecholamine metabolites are best measured in the serum.

• A. True
• B. False
• C. Not sure
• D. Cannot determine

Answer: (B)

Free catecholamines are rapidly cleared from circulation, with very short plasma half-lives, so their levels can fluctuate and are hard to capture with a single measurement. Because of this, measuring them in urine is not as reliable. The more stable markers are the catecholamine metabolites, the metanephrines, which remain in the blood longer and provide a more consistent indication of excess catecholamine activity. In practice, plasma (serum) testing for plasma free metanephrines is preferred for sensitivity in detecting pheochromocytoma, while urinary measurements of catecholamines are less reliable. So the statement is false: free catecholamines are short-lived but are not best measured in urine, and catecholamine metabolites are best measured in plasma.

Free catecholamines are rapidly cleared from circulation, with very short plasma half-lives, so their levels can fluctuate and are hard to capture with a single measurement. Because of this, measuring them in urine is not as reliable. The more stable markers are the catecholamine metabolites, the metanephrines, which remain in the blood longer and provide a more consistent indication of excess catecholamine activity. In practice, plasma (serum) testing for plasma free metanephrines is preferred for sensitivity in detecting pheochromocytoma, while urinary measurements of catecholamines are less reliable. So the statement is false: free catecholamines are short-lived but are not best measured in urine, and catecholamine metabolites are best measured in plasma.