Normal BUN Range for Elderly Men
The normal BUN range for elderly men without kidney disease is 14-23 mg/dL, which is higher than the standard adult range of 10-20 mg/dL. 1
Age-Related Changes in BUN
- BUN levels increase significantly with age in elderly men, with a positive correlation between BUN and advancing age after the seventh decade 1
- The mean BUN level in elderly subjects (≥70 years) is significantly higher than in younger control subjects, reflecting age-related physiological changes 1
- This elevated baseline occurs even in apparently healthy elderly individuals without overt kidney disease 1
Critical Clinical Context: Why Serum Creatinine Alone is Misleading
Never rely on serum creatinine alone to assess kidney function in elderly patients—this is explicitly prohibited by the National Kidney Foundation's K/DOQI guidelines. 2
- A serum creatinine of 1.2 mg/dL may represent a creatinine clearance of 110 mL/min in a young adult but only 40 mL/min in an elderly patient 2
- Age-related muscle mass loss decreases creatinine production independently of kidney function, causing serum creatinine to significantly underestimate renal insufficiency in the elderly 2, 3, 4
- When serum creatinine significantly increases, GFR has already decreased by at least 40% 2
- Among patients with normal serum creatinine measurements, one in five had asymptomatic renal insufficiency when assessed by creatinine clearance methods 2
Proper Assessment of Renal Function in Elderly Men
Calculate creatinine clearance using the Cockcroft-Gault formula for medication dosing decisions, and use MDRD or CKD-EPI equations for diagnosing and staging chronic kidney disease. 2
- The Cockcroft-Gault formula: CrCl (mL/min) = [(140 - age) × weight (kg)] / [72 × serum creatinine (mg/dL)] 2
- The MDRD formula may be the estimation of choice in elderly patients for CKD staging 3
- All formulas systematically underestimate renal function in the oldest patients, but they remain clinically necessary tools that must be used with full awareness of their biases 2
Interpreting BUN in Context
- The normal BUN:creatinine ratio is 10-15:1 5
- A ratio greater than 20:1 suggests prerenal azotemia (dehydration, heart failure, hypovolemia) or increased protein catabolism 5, 6
- A ratio of 10:1 suggests intrinsic renal failure 5
- Disproportionately elevated BUN (>100 mg/dL with modest creatinine elevation) is most common in elderly patients due to their lower muscle mass, and often indicates multifactorial causes including hypovolemia, high protein intake, infection, or hypercatabolic states 6
Common Pitfalls to Avoid
- Do not assume normal renal function based on "normal-appearing" serum creatinine in elderly patients—this is the most dangerous error in geriatric medicine 2, 4
- NSAIDs significantly increase BUN and creatinine levels in elderly patients, with chronic users having 1.9 times higher odds of elevated BUN (>23 mg/dL) 7
- High protein intake, including enteral nutrition, can cause marked BUN elevation in elderly patients with reduced renal reserve, even when serum creatinine appears reassuring 8
- Severe muscle wasting or malnutrition can produce inappropriately low creatinine levels that mask significant kidney dysfunction, making the BUN:creatinine ratio unreliable 4