The kidneys have a big reserve capacity – damage can occur to the kidneys without causing noticeable failure in its functions. Damage to the kidneys can be divided into two types: one-off, or progressive. A one-off damage to the kidney results in acute kidney failure – in this condition the kidney usually recovers and returns to near normal function with time. However slow, continuous kidney damage causes chronic kidney failure. The degree of kidney damage in chronic kidney failure allows us to divide it into five stages:

 

Stage I: >90% normal kidney function

Stage II: 60 – 90% normal kidney function

Stage III: 30 – 60% normal kidney function

Stage IV: 15 – 30% normal kidney function

Stage V: <15% normal kidney function

 

Stage V is often termed end-stage kidney failure where replacement of kidney function is necessary to prevent severe disability and/or death.