A patient has BUN 28 mg/dL and creatinine 1.2 mg/dL. What does this pattern typically indicate?

• A. Acute kidney injury due to nephrotoxins
• B. Chronic kidney disease
• C. Possible prerenal azotemia/dehydration; correlate with fluid status and other labs.
• D. Postrenal obstruction

Answer: (C)

Interpreting these labs hinges on the BUN to creatinine ratio and what it tells you about kidney perfusion. When the kidneys are underperfused, they conserve water and reabsorb more urea, so BUN rises disproportionately compared with creatinine. A BUN of 28 mg/dL with a creatinine of 1.2 mg/dL gives a ratio around 23:1, which is a pattern typical of prerenal azotemia, often due to dehydration or reduced circulating volume.

To confirm, clinicians look at fluid status and additional urine tests. In prerenal states, urine tends to be concentrated (high osmolality) and sodium tends to be low (low urine sodium, FeNa often <1%). This supports the idea that the kidney is trying to preserve volume rather than being damaged at the tissue level.

Other patterns fit different problems: intrinsic kidney injury from nephrotoxins or ATN usually shows a lower BUN/creatinine ratio (often closer to 10–15:1) and higher FeNa with more sodium loss in urine; chronic kidney disease often elevates both BUN and creatinine with a less pronounced ratio; postrenal obstruction can raise both, but the pattern is less specific and depends on duration and severity.

So the pattern you’re seeing points toward prerenal azotemia/dehydration, with further assessment of volume status and targeted urine studies helping to confirm.