A BUN-to-creatinine ratio greater than 20:1 with an elevated creatinine level is most consistent with which type of azotemia?

• A. Renal and Post-renal Azotemia
• B. Pre-renal Azotemia
• C. Hepatic Failure
• D. Dehydration

Answer: (A)

BUN rises more than creatinine when kidney perfusion is low because the tubules reabsorb more urea to conserve water. This makes the BUN/creatinine ratio climb above 20:1 even though creatinine is also elevated due to reduced glomerular filtration. That pattern is classic for prerenal azotemia, which occurs with decreased renal perfusion from causes like dehydration or hypovolemia.

In intrinsic renal (tubular) azotemia, the kidneys lose the ability to reabsorb urea, so the BUN and creatinine rise more evenly and the ratio tends to be nearer the normal range. Postrenal azotemia can show variable ratios depending on the stage, and hepatic failure would not typically produce a high BUN/creatinine ratio because urea production is impaired.

So, a BUN-to-creatinine ratio >20:1 with an elevated creatinine most strongly points to prerenal azotemia due to reduced renal perfusion, with dehydration being a common underlying cause.