<prompt> Chronic Renal Failure is defined as Residual renal functional mass less than:5080205  <response>: Answer is C 20: Function mass less than 20 percent of normal. Pathological Classification of Chronic Kidney DiseaseCKD Diminished Renal Reserve Renal Insufficiency Chronic Renal Failure End-Stage Renal Disease Residual Functional Renal Mass Residual GFR of Normal 50 to 80 percent of Normal 20 to 50 percent of Normal Less than 20 percent of normal Less than 5 percent of normal Signs and Symptoms of Renal Failure are evident in the stage of Renal Insufficiency. 