How do doctors tell if it's a back ache or kidney problems?

Kidney or back: Its hard to tell. Obvious kidney: blood in urine, itching, burning or foul smelling or cloudy urine; obvious spine: numbness, weakness, radiating pains, pain with bending/twisting. Pain right under ribs probably kidney. Pain in the middle of back directly over spine, probably back. If in question, exam, labs, and/or studies needed.