In acute kidney injury, which lab pattern is described as elevated BUN and creatinine with a ratio less than 20, commonly due to iatrogenic causes?

• A. Elevated BUN and creatinine with BUN/Cr ratio < 20
• B. Elevated BUN and creatinine with BUN/Cr ratio > 20
• C. Normal BUN and elevated creatinine
• D. Low BUN and creatinine

Answer: (A)

When assessing AKI, the BUN to creatinine ratio helps distinguish perfusion-related injury from intrinsic kidney injury. In prerenal states, reduced perfusion leads to increased BUN reabsorption, so the ratio tends to be higher (often >20). In intrinsic renal injury, such as nephrotoxic or iatrogenic tubular damage, both BUN and creatinine rise but the ratio remains normal or below 20 because urea reabsorption is less affected. Therefore, elevated BUN and creatinine with a BUN/creatinine ratio under 20 points to intrinsic kidney injury, commonly from iatrogenic nephrotoxic causes. Patterns with ratio > 20 suggest prerenal azotemia; other atypical patterns don’t fit the typical intrinsic AKI picture.