From the Guidelines
Elevated BUN and creatinine levels are primarily associated with conditions that impair kidney function, such as acute kidney injury, chronic kidney disease, urinary tract obstruction, glomerulonephritis, diabetic nephropathy, and polycystic kidney disease, as stated in the 2021 study by the Journal of the American College of Radiology 1. These conditions reduce the kidneys' ability to filter waste products from the blood, causing BUN and creatinine to accumulate. Dehydration and high-protein diets can also raise these values without indicating kidney disease. Some key points to consider include:
- Acute kidney injury (AKI) is defined as an increase in creatinine by 0.3 mg/dL within 48 hours or an increase in serum creatinine to 1.5 times baseline, and is often multifactorial, with prerenal, renal, and postrenal causes 1.
- Chronic kidney disease (CKD) is defined as an abnormality of kidney structure or function, present for >3 months, with health consequences, and is categorized into five stages based on estimated GFR 1.
- Decreased BUN and creatinine levels are less common but may occur in conditions like pregnancy, severe liver disease, malnutrition, and SIADH (syndrome of inappropriate antidiuretic hormone secretion). When evaluating abnormal BUN and creatinine levels, it's essential to consider the BUN/creatinine ratio, with ratios above 20:1 suggesting pre-renal causes like dehydration, while lower ratios may indicate intrinsic kidney damage, as noted in the 2003 study by the Annals of Internal Medicine 1. These laboratory values should always be interpreted alongside clinical symptoms, urinalysis, and imaging studies for accurate diagnosis. Some conditions that may cause low BUN and creatinine levels include:
- Pregnancy, due to increased glomerular filtration rate
- Severe liver disease, due to reduced urea production
- Malnutrition, due to decreased muscle mass and protein intake
- SIADH, due to syndrome of inappropriate antidiuretic hormone secretion.
From the Research
Renal and Genitourinary Conditions Associated with Elevated BUN and Cr Levels
- Acute kidney injury (AKI) is associated with elevated Blood Urea Nitrogen (BUN) and Creatinine (Cr) levels 2, 3, 4
- Pre-renal azotemia, characterized by a high BUN:Cr ratio, is associated with elevated BUN and Cr levels 2, 4
- Obstructive nephropathy, a condition caused by obstruction in the urinary tract, can lead to acute kidney injury and elevated BUN and Cr levels 5, 6
- Malignancy, urolithiasis, and other causes of obstructive uropathy can also lead to elevated BUN and Cr levels 6
Renal and Genitourinary Conditions Associated with Decreased BUN and Cr Levels
- There is limited evidence to suggest that certain renal and genitourinary conditions are associated with decreased BUN and Cr levels
- However, it is worth noting that a low BUN:Cr ratio has been associated with a lower mortality rate in patients with acute kidney injury 4