Final answer:
Creatinine is the lab value not affected by diet that is used as an indicator of renal failure.
Step-by-step explanation:
The lab value that is not affected by diet and is used as an indicator of renal failure is Creatinine.
Although Blood Urea Nitrogen (BUN) is also used to assess renal function, it can be influenced by diet and other factors, making Creatinine a more reliable indicator. Creatinine is a waste product produced by muscle metabolism and it is not significantly influenced by dietary intake.
Other lab values mentioned in the question, such as Glucose and Potassium, are not specific indicators of renal failure, although they can be affected by kidney function to some extent.