Urea – Creatinine Ratio

The relationship of urea and creatine is dependent on serum laboratory units used to determine the cause of acute kidney injury.

• In the US the urea is expressed as BUN (Blood Urea Nitrogen) in mg/dL. Elsewhere Urea (U) is expressed as mmol/L
• Similarly Creatinine (Cr) is expressed as mg/dL in the US and µmol/L elsewhere

Therefore two ratio’s exist to compare serum Urea and Creatinine levels

• BUN : Cr ratio with US units of mg/dL : mg/dL
• Urea: Cr ratio ith SI Units of mmol/L: µmol/L (providing Urea is >10mmol/L)
• Cr: Urea ratio with SI Units of µmol/L: mmol/L (providing Urea is >10mmol/L)

References:

• Morgan DB, Carver ME, Payne RB. Plasma creatinine and urea: creatinine ratio in patients with raised plasma urea. Br Med J. 1977 Oct 8;2(6092):929-32. PMID 912370
• Witting MD, Magder L, Heins AE, Mattu A, Granja CA, Baumgarten M. ED predictors of upper gastrointestinal tract bleeding in patients without hematemesis. Am J Emerg Med. 2006 May;24(3):280-5. PMID 16635697
• Urashima M, Toyoda S, Nakano T, Matsuda S, Kobayashi N, Kitajima H, Tokushige A, Horita H, Akatsuka J, Maekawa K. BUN/Cr ratio as an index of gastrointestinal bleeding mass in children. J Pediatr Gastroenterol Nutr1992 Jul;15(1):89-92. PMID 1403455.
• Feinfeld DA, Bargouthi H, Niaz Q, Carvounis CP. Massive and disproportionate elevation of blood urea nitrogen in acute azotemia. Int Urol Nephrol. 2002;34(1):143-5. PMID 12549657

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