Which condition may raise BUN without increasing creatinine?

Which condition may raise BUN without increasing creatinine?

• A. Renal Failure
• B. Dehydration (BUN ONLY)
• C. Liver disease
• D. Malabsorption syndromes

Answer: (B)

The key idea is that an increased BUN with a normal or non-elevated creatinine points to a prerenal, perfusion-related issue rather than actual kidney injury. Dehydration reduces circulating volume and renal perfusion, so the kidneys respond by reabsorbing more urea in an effort to conserve water. This raises BUN, while creatinine—produced at a steady rate and filtered by the glomerulus—may stay normal initially, so the BUN increase occurs without a corresponding rise in creatinine. This pattern also pushes the BUN:creatinine ratio higher. In contrast, true kidney injury from renal failure tends to elevate both BUN and creatinine because filtration is impaired. Liver disease reduces the liver’s ability to produce urea, which can lower or normalize BUN despite kidney function issues. Malabsorption or malnutrition can lower urea production as well, rather than raising BUN.

The key idea is that an increased BUN with a normal or non-elevated creatinine points to a prerenal, perfusion-related issue rather than actual kidney injury. Dehydration reduces circulating volume and renal perfusion, so the kidneys respond by reabsorbing more urea in an effort to conserve water. This raises BUN, while creatinine—produced at a steady rate and filtered by the glomerulus—may stay normal initially, so the BUN increase occurs without a corresponding rise in creatinine. This pattern also pushes the BUN:creatinine ratio higher.

In contrast, true kidney injury from renal failure tends to elevate both BUN and creatinine because filtration is impaired. Liver disease reduces the liver’s ability to produce urea, which can lower or normalize BUN despite kidney function issues. Malabsorption or malnutrition can lower urea production as well, rather than raising BUN.