creatinine serum uln times institutional concentration days prior equal levels creatinine upper limit normal times institutional serum uln institution age amylase lipase uln serum normal institutional days registration prior limits potassium limits normal meq serum range institutional institution wnl supplementation limits creatinine normal institutional upper serum uln times troponin days limits bilirubin normal upper total uln serum institutional times ast renal creatinine function uln serum adequate times defined normal mg