Which BUN/creatinine ratio corresponds to intrarenal dysfunction?

• A. 10-20:1
• B. Greater than 20:1
• C. <10:1
• D. 5-15:1

Answer: (C)

The BUN to creatinine ratio reflects how the kidney handles urea reabsorption. In prerenal states, low renal perfusion causes the kidneys to conserve water and reabsorb more urea, so BUN rises disproportionately to creatinine and the ratio is typically >20:1. In intrinsic (intrarenal) dysfunction, tubular damage impairs the kidney’s ability to reabsorb BUN, so BUN doesn’t rise as much relative to creatinine, yielding a normal or low ratio. Because of this impaired reabsorption, intrinsic kidney injury often presents with a BUN/creatinine ratio around 10:1 or lower. Therefore, a ratio below 10:1 best fits intrarenal dysfunction.