Which statement best describes prerenal azotemia in relation to BUN and creatinine?

Which statement best describes prerenal azotemia in relation to BUN and creatinine?

• A. BUN increases more than creatinine
• B. Creatinine increases more than BUN
• C. BUN and creatinine increase equally
• D. BUN decreases

Answer: (A)

In prerenal azotemia, reduced kidney perfusion triggers the kidney to conserve water, which increases the reabsorption of urea in the proximal tubule. This causes the BUN to rise disproportionately compared with creatinine, because creatinine is filtered and not reabsorbed to a significant extent. The net effect is a higher BUN relative to creatinine, often with a BUN/creatinine ratio above about 20:1. So the statement that BUN increases more than creatinine best describes this pattern. If creatinine rose more than BUN or they rose equally, that would point to different types of kidney injury; a decrease in BUN would not fit prerenal azotemia.

In prerenal azotemia, reduced kidney perfusion triggers the kidney to conserve water, which increases the reabsorption of urea in the proximal tubule. This causes the BUN to rise disproportionately compared with creatinine, because creatinine is filtered and not reabsorbed to a significant extent. The net effect is a higher BUN relative to creatinine, often with a BUN/creatinine ratio above about 20:1. So the statement that BUN increases more than creatinine best describes this pattern. If creatinine rose more than BUN or they rose equally, that would point to different types of kidney injury; a decrease in BUN would not fit prerenal azotemia.