Renal or post-renal azotemia is suggested by which pattern of BUN and creatinine?

• A. High BUN and high creatinine
• B. High BUN and normal creatinine
• C. Normal BUN and high creatinine
• D. Low BUN and low creatinine

Answer: (A)

When the kidneys aren’t filtering waste properly, both substances that reflect kidney function rise in the blood. In renal (intrinsic) failure or post-renal obstruction, the kidney’s ability to excrete nitrogenous waste is impaired, so both BUN and creatinine accumulate. This pattern—elevated BUN together with elevated creatinine—signals that the problem lies within the kidney itself or downstream of it, rather than a drop in blood flow to the kidneys alone. In prerenal azotemia, BUN tends to rise disproportionately compared with creatinine because the kidneys reabsorb more urea during reduced perfusion, so the BUN/creatinine ratio is high rather than both values rising together. Thus, high BUN and high creatinine best indicate renal or post-renal azotemia.