MedSchool: Ace Your OSCEsThe Medical Company
GET - On the App Store
Renal Function




  • Urea is a nitrogenous waste product that allows the kidneys to excrete nitrogen; it also drives the countercurrent exchange system within the nephron.
      • Normal Range

      • 3.0 - 8.0 mmol/L
    • Key Concepts

    • Urea is less reliable than creatinine as a marker of GFR, as levels are more likely to be variable.
    • 40-50% reabsorbed by the tubules;
    • Urea is mainly useful when the serum urea is disproportionately high compared to elevated creatinine - see urea:creatinine ratio for more information

Elevated Urea

  • An elevated serum urea may be an indicator of renal injury, though it may also be raised in the setting of dehydration, protein breakdown or a protein load.
    • Causes of Elevated Urea

    • Renal Failure

    • Acute kidney injury
    • Chronic kidney disease
    • Other Causes

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

Reduced Urea

    • Causes of Reduced Urea

    • Low protein intake - low protein diet, malnutrition, malabsorption, alcoholism
    • Liver disease
    • Pregnancy
Want more info like this?
  • Your electronic clinical medicine handbook
  • Guides to help pass your exams
  • Tools every medical student needs
  • Quick diagrams to have the answers, fast
  • Quizzes to test your knowledge
Sign Up Now


 Bellomo R, Kellum JA, Ronco C. Acute kidney injury. The Lancet. 2012 Aug 31;380(9843):756-66.
Harris MD, Siegel LB, Alloway JA. Gout and hyperuricemia. American family physician. 1999 Feb;59(4):925-34.
 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.
Traynor J, Mactier R, Geddes CC, Fox JG. How to measure renal function in clinical practice. BMJ: British Medical Journal. 2006 Oct 7;333(7571):733.