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|Methodology:||Liquid Chromatography / Tandem Mass Spectrometry (LC/MS/MS)|
|Released:||24-72 hours after setup at PeaceHealth Laboratories’ reference lab.|
|Specimen Collection Details|
|Collection:||24-hour or random urine. Refrigerate during collection, storage and transport. NOTE: Patient should abstain from medications for 72 hours prior to collection.|
|Handling:||5 mL aliquot from a well-mixed 24-hour or random urine collection. Record total volume and collection time interval on transport container and on requisition. Adequate refrigeration is the most important aspect of specimen preservation. Stability is enhanced at pH 2.0-3.0. A pH lower than 2.0 may cause assay interference.|
|Stability:||24 hours ambient, 14 days refrigerated, or 1 month frozen.|
|Standard Volume:||5 mL urine.|
|Minimum Volume:||1.5 mL urine.|
|Comments:||Smaller increases in normetanephrine and/or metanephrine concentrations (less than two times the upper reference limit) usually are the result of physiological stimuli, drugs, or improper specimen collection. Significant elevation of one or both metanephrines (3 or more time the upper reference limit) is associated with an increased probability of a neuroendocrine tumor.
Secreting neuroendocrine tumors are typically associated with metanephrine or normetanephrine concentrations several times higher than the upper reference intervals. Other reasons for elevated concentrations include intense physical activity, life-threatening illness, and drug interferences. Essential hypertension is often associated with slight elevations (metanephrine less than 700 µg/day and normetanephrine less than 900 µg/day). Other reasons for slight and moderate elevations include emotional and physical stress, and improper specimen collection.
Medications that may physiologically interfere with metanephrines include amphetamines and amphetamine-like compounds, appetite suppressants, bromocriptine (Parlodel), buspirone (Buspar), caffeine, carbidopa-levodopa (Sinemet), clonidine (Catapres, Dixarit), dexamethasone (Dexacort), diuretics (in doses sufficient to deplete sodium), methyldopa (Aldomet), MAO inhibitors, nose drops, propafenone (Rythmol), tricyclic antidepressants, and vasodilators. The effects of some drugs on catecholamine metabolite results may not be predictable.
|The metanephrines-to-creatinine ratios will be reported when the patient is under 18 years, or the urine collection is random or other than a 24-hour, or the urine volume is less than 400 mL/24 hours.
Ratios-to-creatinine may be useful for evaluation of patients younger than 18 years when the urine collection is random or other than a 24-hour, or the urine volume is less than 400 mL/24 hours.
Mass per day (mg or µg) calculations are not reported when the urine collection is random or other than a 24-hour, or the urine volume is less than 400 mL/24 hours.