the meaning of "what's up" is different in british english and in american english. American meaning is like "how are you?" so you can translate it in italian using "Come va?". British meaning is like "what's wrong?" and you can say "Cosa c'è che non va?" in italian. In british english "what's up" is not a greeting, so if you need to greet someone you must use "Come va?".

Hello Adelaide, Whats up ? = Cosa c'è?