What are the normal levels for normetanephrines (NMN), a metabolite of norepinephrine?

From the Research

Normal levels for normetanephrines vary slightly depending on the laboratory and testing method used, but generally, plasma free normetanephrine levels should be less than 0.9 nmol/L (approximately 164 pg/mL) and for 24-hour urine collections, normal normetanephrine levels are typically below 900 μg/24 hours, as updated reference intervals have been proposed to reduce false positives without compromising test sensitivity for true pheochromocytoma 1.

Key Points to Consider

• The updated reference intervals for urine normetanephrine aim to minimize false positives while maintaining test sensitivity for pheochromocytoma diagnosis 1.
• Plasma free normetanephrine levels and 24-hour urine collections are used to diagnose conditions such as pheochromocytoma, paraganglioma, or other catecholamine-secreting tumors.
• Certain factors can falsely elevate normetanephrine levels, including stress, strenuous exercise, certain medications, caffeine consumption, and alcohol withdrawal.
• Patients should avoid these potential interfering factors before testing when possible to ensure accurate results.
• If elevated levels are found, repeat testing or additional diagnostic procedures may be recommended to confirm findings.

Relevant Guidelines and Studies

• The Endocrine Society clinical practice guideline recommends initial biochemical testing for pheochromocytoma and paraganglioma (PPGL) to include measurements of plasma free or urinary fractionated metanephrines, considering preanalytical factors that may lead to false-positive or false-negative results 2.
• A study found that plasma free metanephrine and normetanephrine levels are frequently elevated in patients with chronic kidney disease, particularly those on dialysis, which may lead to false positives in pheochromocytoma screening 3.
• Another study determined that the measurement of plasma free metanephrines with LC-MS/MS is not affected by the use of β-blockers, diuretics, and ACE inhibitors, making it unnecessary to withdraw these medications before testing 4.