Since the abbreviation for the fractional excretion of sodium is FENa, all the cool kids call it the fena (rhymes with Gina). So the fractional excretion of urea by extension is the FEUrea, which doesn't quite role off the tongue.
Last month on vacation, we had dinner with an old friend from medical school, now a hospitalist outside Atlanta, and she started talking about ordering febuns. I asked her what a febun was and she explained the fractional excretion of BUN. Ahhh.
My wife, who hated driving my car with the license plate FE UREA immediately declared febun both cute and the official title, at least in the Topf household.