Ahh, there are loads of reasons to piss in a cup! We can diagnose everything from infections and metabolic conditions, right through to some types of brain damage and certain types of tumors from urine samples.

Interestingly, the word "mellitus" in "diabetes mellitus" is Latin for "sweetened with honey", because the urine of sufferers of this disease tastes sweet like honey, which is how it used to be diagnosed before modern glucose testing.