Renal Function
Renal Function
 

Urea:Creatinine Ratio

 
 
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Overview

  • In the presence of raised creatinine, urea disproportionately higher than creatinine suggests a prerenal cause such as hypovolaemia, heart failure or shock.
    • Interpretation

    • Elevated ratio: >100:1
    • Reduced ratio: <40:1

Elevated Urea:Creatinine Ratio

  • A urea:creatinine ratio >100:1 is commonly used as a marker of prerenal renal failure. Any cause of isolated urea elevation may also elevate the ratio.
    • Causes of Elevated Urea:Creatinine Ratio

    • Prerenal renal failure - hypovolaemia, sepsis, renal venoconstriction
    • Dehydration
    • Protein load - GI bleed (especially upper GI), high protein diet
    • Catabolic state - trauma, sepsis, starvation, corticosteroids

Reduced Urea:Creatinine Ratio

    • Causes of Reduced Urea:Creatinine Ratio

    • Severe liver failure
    • Low protein intake - low protein diet, malnutrition, malabsorption, alcoholism
    • Muscle breakdown - body building, rhabdomyolysis
    • Pregnancy
 
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 Koyner JL. Assessment and diagnosis of renal dysfunction in the ICU. CHEST Journal. 2012 Jun 1;141(6):1584-94. Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF, Feldman HI, Kusek JW, Eggers P, Van Lente F, Greene T, Coresh J. A new equation to estimate glomerular filtration rate. Annals of internal medicine. 2009 May 5;150(9):604-12. Nankivell BJ. Creatinine Clearance and the Assessment of Renal Function. Australian Prescriber. 2001; 24: 15-17. Richards RJ, Donica MB, Grayer D. Can the Blood Urea Nitrogen/Creatinine Ratio Distinguish Upper From Lower Gastrointestinal Bleeding?. Journal of clinical gastroenterology. 1990 Oct 1;12(5):500-4. Samra M, Abcar AC. False estimates of elevated creatinine. The Permanente Journal. 2012;16(2):51. Schold JD, Navaneethan SD, Jolly SE, Poggio ED, Arrigain S, Saupe W, Jain A, Sharp JW, Simon JF, Schreiber MJ, Nally JV. Implications of the CKD-EPI GFR estimation equation in clinical practice. Clinical Journal of the American Society of Nephrology. 2011 Mar 1;6(3):497-504. Shlipak MG, Katz R, Kestenbaum B, Fried LF, Newman AB, Siscovick DS, Stevens L, Sarnak MJ. Rate of kidney function decline in older adults: a comparison using creatinine and cystatin C. American journal of nephrology. 2009;30(3):171-8.
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