BUN/Creatinine Ratio Calculation
To calculate the BUN/creatinine ratio with a BUN of 60 mg/dL and creatinine of 3.2 mg/dL, simply divide BUN by creatinine: 60 ÷ 3.2 = 18.75.
How to Calculate
- The calculation is straightforward: divide the BUN value by the serum creatinine value 1
- In your case: 60 mg/dL ÷ 3.2 mg/dL = 18.75
- This ratio is expressed as a simple number without units 1
Interpretation of Your Result
- Your ratio of 18.75 falls within the normal range of 10:1 to 20:1, suggesting intrinsic renal dysfunction rather than pre-renal azotemia 1, 2
- The normal BUN/creatinine ratio is typically 10-15:1, with values up to 20:1 still considered within normal limits 1, 3
Clinical Significance of This Ratio
- A ratio <20:1 in the setting of elevated BUN (60 mg/dL) and creatinine (3.2 mg/dL) suggests acute or chronic renal failure where both values rise proportionally 1
- A ratio >20:1 would suggest pre-renal azotemia (dehydration, heart failure, shock), but your ratio does not meet this threshold 1, 2
- Both your BUN and creatinine are significantly elevated (normal BUN: 10-20 mg/dL; normal creatinine: 0.6-1.2 mg/dL), indicating substantial kidney dysfunction 1
Important Clinical Considerations
- The BUN/creatinine ratio should never be interpreted in isolation—always calculate estimated GFR using validated formulas like MDRD or CKD-EPI for accurate kidney function assessment 4, 5
- Age-related muscle mass changes can affect creatinine levels in older adults, potentially masking the true severity of renal dysfunction 6, 4
- Multiple factors can affect this ratio beyond renal perfusion, including protein intake, catabolic state, gastrointestinal bleeding, steroid use, and sepsis 2
Next Steps for Assessment
- Calculate eGFR immediately using CKD-EPI or MDRD formulas for more accurate staging of kidney disease 4, 5
- Assess hydration status, recent protein intake, and presence of hypercatabolic states (infection, sepsis, steroid use) that could affect the ratio 4, 2
- Obtain urinalysis to evaluate for proteinuria, hematuria, or casts that indicate specific kidney pathology 4
- Review medications for nephrotoxic agents and check for risk factors including diabetes, hypertension, or family history of kidney disease 4