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Avoid patient stress. Many drugs (reserpine and alpha methyldopa, levodopa, monoamine oxidase inhibitors, and sympathomimetic amines) may interfere and should be discontinued two weeks prior to specimen collection. Nose drops, sinus and cough medicines, bronchodilators and appetite suppressants, α2-agonists, calcium channel blockers, converting enzyme inhibitors, bromocriptine, phenothiazine, tricyclic antidepressants, α- and β-blockers, and labetalol may interfere.1 Mandelamine® interferes, but thiazides do not. Caffeine products should be avoided before and during collection. The patient should not be subjected to hypoglycemia or exertion. Increased intracranial pressure and clonidine withdrawal can cause false-positive results.
Liquid chromatography/tandem mass spectrometry (LC/MS-MS)
False-negatives and false-positives occur. Since a 24-hour urine collection represents a longer sampling time than a random, or symptom-directed serum sample, and because catecholamine secretion by pheochromocytomas is intermittent, the 24-hour urine test may detect some cases missed by a blood or random urine level.
Specimen with no preservative; original container with pH >5
Adjust pH to <5 with 6N HCl.