Complete Blood Count

• Typically, blood work that is run on your cat involves at the minimum a complete blood count, or CBC. The BUN and creatinine levels are included in the CBC.
  
  

Indications

• BUN and creatinine are both indicative of urinary and kidney function, although elevated levels of one or both can sometimes show dehydration, muscle damage, or simply dietary considerations, according to the Merck Veterinary Manual.
  
  

BUN

• The blood urea nitrogen, or BUN, refers to the waste product that is excreted through the kidneys. A normal BUN in a feline is around 25. A cat with well-controlled kidney failure typically produces a BUN of 60 to 80. At the time of kidney failure diagnosis a typical BUN reading can be as high as 300.
  
  

Creatinine

• Also a waste product excreted though the kidneys, creatinine is an overall indicator of declining kidney function. A normal creatinine level is around 2.0, whereas a cat with kidney failure can have a creatinine level as high as 5.0.
  
  

Important Considerations

• Although BUN and creatinine levels are good indicators of feline kidney function, Merck says that by the time the blood work shows elevated levels, a good deal of renal dysfunction has already occurred. It is important to notice changes in your cat's behaviors and to have regularly scheduled veterinarian visits, in addition to the blood work.