Differential Diagnosis for Elevated BUN with Normal Creatinine

• Single most likely diagnosis:
  • Dehydration: This is the most common cause of an elevated BUN with a normal creatinine level. Dehydration leads to a decrease in blood volume, which in turn reduces blood flow to the kidneys, causing an increase in BUN.
• Other Likely diagnoses:
  • High protein diet: Consuming a diet high in protein can increase BUN levels because the kidneys have to work harder to filter out the waste products of protein metabolism.
  • Gastrointestinal bleeding: Bleeding in the gastrointestinal tract can lead to an increase in BUN due to the absorption of blood, which is high in protein.
  • Heart failure: Reduced cardiac output can lead to decreased renal perfusion, resulting in elevated BUN levels.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Prerenal azotemia due to renal artery stenosis: Although less common, this condition can lead to reduced blood flow to the kidneys, causing an elevation in BUN.
  • Sepsis: Sepsis can cause a decrease in blood flow to the kidneys, leading to elevated BUN levels.
• Rare diagnoses:
  • Rhabdomyolysis with minimal creatinine elevation: Although creatinine is often elevated in rhabdomyolysis, there can be cases where the creatinine level remains normal or near-normal despite significant muscle breakdown.
  • Early stages of kidney disease: Certain kidney diseases can present with an isolated elevation in BUN before significant changes in creatinine levels are observed.