What substances interfere with the plasma metanephrine test?

Metanephrine: You should discontinue Epinephrine and epinephrine-like drugs for at least 1 week before the test, stop using Acetaminophen 48 hours beforehand, and fast for 8-10 hours prior to collection. It is especially important not to have any caffeine containing food (soda, chocolate), coffee (including decaf), tobacco (smoking cigarettes or cigars), tea, or alcohol for at least 4 hours before specimen coll.

Many substances: The assay for free metanephrines is sensitive, but not specific. Many drugs containing Epinephrine compounds (such as sudaphed and related ones), as well as some anti-depressants (especially mono amine oxidase inhibitors) will affect the results. Tyrosine containing foods (bananas, cheese, etc.) often interfere with levels, as does smoking, some local anesthetics and Acetaminophen may as well.