From the Guidelines
An elevated BUN/creatinine ratio is typically caused by pre-renal conditions, such as dehydration, heart failure, or gastrointestinal bleeding, which increase blood urea nitrogen disproportionately to creatinine.
Common Causes
- Dehydration, which reduces kidney perfusion and increases urea reabsorption
- Gastrointestinal bleeding, where blood proteins are broken down into urea in the gut
- High-protein diets that provide more nitrogen for urea formation
- Catabolic states like burns or fever that increase protein breakdown
- Certain medications such as corticosteroids, tetracyclines, and NSAIDs
- Heart failure, which can reduce kidney perfusion, as noted in the 2016 ESC guidelines for the diagnosis and treatment of acute and chronic heart failure 1.
Management and Diagnosis
Management depends on the underlying cause—rehydration for dehydration, stopping offending medications, or treating the primary condition like heart failure with appropriate medications, as suggested by the acc/aha 2007 guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery 1. The ratio is elevated because urea is more readily reabsorbed in the kidneys than creatinine when blood flow is reduced, making it a useful indicator of pre-renal issues versus intrinsic kidney damage, where both values typically rise proportionally. Regular assessment of renal function, including measurement of creatinine, BUN, and electrolytes, is crucial in patients with heart failure, as recommended in the 2016 ESC guidelines 1.
From the Research
Causes of Elevated BUN/CR Ratio
- Elevated blood urea nitrogen-to-creatinine (BUN/CR) ratio can be caused by various factors, including decompensated heart failure 2 and chronic heart failure 3
- In patients with decompensated heart failure, an elevated admission BUN/CR ratio is associated with an increased risk of in-hospital improvement in renal function (IRF) with treatment, as well as post-discharge worsening renal function 2
- In patients with chronic heart failure, an elevated BUN-to-creatinine ratio is associated with a heightened risk of hospitalization and all-cause death, independent of glomerular filtration rate (GFR) 3
Associated Risks
- An elevated BUN/CR ratio is associated with a substantial risk of death in patients with renal dysfunction (estimated glomerular filtration rate <45) 2
- The coexisting presence of an elevated BUN/CR ratio and reduced GFR (<60 ml/min/1.73 m(2)) tends to pose a synergistic risk for hospitalization and all-cause death in patients with chronic heart failure 3
Clinical Implications
- An elevated admission BUN/CR ratio can identify decompensated heart failure patients likely to experience IRF with treatment, providing proof of concept that reversible renal dysfunction may be a discernible entity 2
- Elevated BUN/CR ratio can be used as a prognostic marker to identify patients with chronic heart failure at increased risk of hospitalization and all-cause death 3