An elevated ratio of serum BUN or urea to serum creatinine may localize gastrointestinal bleeding to the upper GI tract. The increase in BUN or urea is due to resorption of the nitrogen load.
BUN to creatinine ratio in mg/mg =
= (serum BUN in mg/dL) / (serum creatinine in mg/dL)
urea to creatinine ratio in µmol/µmol =
= (serum urea in mmol/L) / (serum creatinine in µmol/L) =
= (serum urea in µmol/L) * 1000 / (serum creatinine in µmol/L)
Author
Population
Ratio
Cutoff for Upper GI Hemorrhage
Richards et al
adult
BUN to creatinine
>= 36
Felber et al
pediatric to 18 years
BUN to creatinine
> 30
Ernst et al
adult
BUN to creatinine
> 36
Olsen and Andreassen
adult
urea to creatinine
> 90
Snook et al
adult
urea to creatinine
>= 100
Performance:
• Ernst et al reported a ratio > 36 had a sensitivity of 28% and specificity of 83%.
• Felber et al reported a ratio > 30 in children had a sensitivity of 39% and specificity of 100%.
• If the ratio is increased, then the patient likely has upper GI hemorrhage. However, a ratio below the cutoff can be seen in either upper or lower GI hemorrhage.
To read more or access our algorithms and calculators, please log in or register.
