Small increases in catecholamines (less than 2 times the upper reference limit) usually are the result of physiological stimuli, drugs or improper specimen collection. Significant elevation of one or more catecholamines (2 or more times the upper reference limit) is associated with an increased probability of a neuroendocrine tumor. Measurement of plasma or urine fractionated metanephrines provide better diagnostic sensitivity than measurement of catecholamines.   Medications which may interfere with catecholamines and metabolites include amphetamines and amphetamine-like compounds, appetite suppressants, bromocriptine, buspirone, caffeine, carbidopa levodopa (Sinemet), clonidine, dexamethasone, diuretics (in doses sufficient to deplete sodium), ethanol, isoproterenol, labetalol, methyldopa (Aldomet), MAO inhibitors, nicotine, nose drops, propafenone (Rythmol, reserpine, theophylline, tricyclic antidepressants and vasodilators. The effects of drugs on catecholamine results may not be predictable.   A reference range is not provided by reference laboratory for patients under 2 days of age.