Table 4.

Factors associated with false positive and false negative testing of metanephrines.

False positives
Medications (3)
Calcium channel blockers
Beta blockers
Mood stabilizers: tricyclic antidepressant, buspirone
Sympathomimetics: amphetamine, ephedrine
Stimulants: caffeine, nicotine
Dopaminergic agents: levodopa, alpha-methyldopa
Acetaminophen
Age
Increase in plasma metanephrines with age (51)
Posture
Increase in plasma metanephrines in seated versus supine position (52, 53)
Exercise (52)
High catecholamine diet (54)
Hypertension (3)
Obstructive sleep apnea (53, 55)
Stroke (3)
Renal impairment (56)
False negatives
Small tumors, usually <2 cm in size in normotensive patients being screened initially or for recurrence
Dopamine-secreting tumors