From the Guidelines
Elevated Blood Urea Nitrogen (BUN) levels are primarily caused by kidney disease or reduced kidney function, dehydration, and increased protein breakdown, as well as certain medications such as ACE inhibitors, ARBs, and NSAIDs, which can affect kidney function and urea excretion. The causes of high BUN levels can be multifactorial, including:
- Kidney disease or reduced kidney function, such as acute kidney injury, chronic kidney disease, or urinary tract obstruction, which impairs the kidneys' ability to filter urea from the blood 1
- Dehydration, which decreases blood volume and reduces kidney perfusion, leading to less efficient urea excretion 1
- Increased protein catabolism from conditions like gastrointestinal bleeding, high-protein diets, or tissue breakdown, which produces more urea and raises BUN levels 1
- Certain medications, including some antibiotics, diuretics, and NSAIDs, which can affect kidney function and elevate BUN levels 1
- Heart failure, which can indirectly cause high BUN by reducing blood flow to the kidneys 1 It is essential to address the underlying cause of elevated BUN levels, whether through increasing fluid intake for dehydration, adjusting medications, treating kidney disease, or managing other contributing conditions, to improve patient outcomes and reduce morbidity and mortality. Some key considerations in managing elevated BUN levels include:
- Monitoring blood chemistry frequently and serially until potassium and creatinine have plateaued 1
- Avoiding NSAIDs unless essential, as they can worsen kidney function and increase BUN levels 1
- Discontinuing calcium-channel blockers unless absolutely necessary, as they can be potentially harmful in patients with systolic heart failure 1
- Considering specialist advice before stopping ACE inhibitors or ARBs, as clinical deterioration is likely if treatment is withdrawn 1
From the Research
Causes of Elevated Blood Urea Nitrogen (BUN) Levels
- Pre-renal azotemia, which can be caused by factors such as hypovolemia, congestive heart failure, and septic or hypovolemic shock 2
- Increased protein catabolism or excessive protein load 2
- Renal failure, although in this case BUN and serum creatinine usually rise in tandem 2
- High protein intake, particularly in elderly patients or those in intensive care units 2
- Infection, which was present in 14 out of 19 patients with severely disproportionate BUN:Cr ratios in one study 2
- Use of high-dose steroids, which was a contributing factor in two patients with elevated BUN levels 2
- Gastrointestinal bleeding, which was present in two patients with elevated BUN levels 2
- HIV infection, which was present in two patients with elevated BUN levels 2
- Heart failure, which has been associated with elevated BUN levels and increased risk of cardiovascular disease 3, 4, 5, 6
- Loop diuretic use, which has been associated with increased mortality in patients with elevated BUN levels 5
- Haemoconcentration, which can affect the predictive value of the BUN/creatinine ratio in patients with heart failure 4
Factors Associated with Elevated BUN Levels
- Age, with elderly patients being more likely to have elevated BUN levels 2
- Serum albumin levels, with lower levels being associated with elevated BUN levels 2
- Total lymphocyte count, with lower counts being associated with elevated BUN levels 2
- Blood urea nitrogen/creatinine ratio, which can identify patients at high risk of renal dysfunction and cardiovascular disease 4, 6