The Cardiovascular
ToolsCalculators

BUN:Creatinine Ratio

Ratio used to help distinguish prerenal from intrinsic azotaemia.

BUN:Creatinine Ratio
Blood urea nitrogen (BUN)
mg/dL
Serum creatinine
mg/dL
Complete the fields above to see the result.

When to use

  • Adjunct to assessing the cause of an elevated creatinine or acute kidney injury.

Formula

Ratio = BUN (mg/dL) ÷ serum creatinine (mg/dL). If urea is reported in mmol/L, BUN (mg/dL) = urea (mmol/L) × 2.8.

Pearls and pitfalls

  • A ratio > 20 also occurs with upper GI bleeding, high protein intake or catabolism.
  • Low ratios accompany low protein intake, liver disease and rhabdomyolysis.

References

  1. Rose BD, Post TW. Clinical Physiology of Acid-Base and Electrolyte Disorders. 5th ed. McGraw-Hill; 2001.