Renal Function
Renal Function
 

Creatinine

 
 
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Overview

      • Normal Range

      • 50 - 120 µmol/L
    • Key Concepts

    • Creatinine is mainly produced by creatine metabolism from muscle breakdown; it is also present in dietary sources like cooked meat
    • Approximately 15% of creatinine is actively secreted into the tubules
    • Patients with stable renal function will have stable creatinine levels with daily variability ~8%

Elevated Creatinine

  • Elevated serum creatinine is most commonly used as a marker of renal injury, though it is important to remember other causes. Patients who have recently eaten meat or who are undergoing muscle breakdown may have an elevated creatinine that gives a false indication of their true renal function. Certain medications (particularly trimethoprim) can elevate the creatinine without causing renal failure.
    • Causes of Elevated Creatinine

    • Renal Failure

    • Acute kidney injury
    • Chronic kidney disease
    • Other Causes

    • Creatinine intake - cooked meat
    • Muscle breakdown - body building, rhabdomyolysis
    • Reduced creatinine secretion - trimethoprim, ranitidine
    • Assay interference - ketosis, hyperbilirubinaemia, cefoxitin

Reduced Creatinine

  • Serum creatinine is commonly reduced in the context of muscle loss or low protein intake; in these situations the creatinine is a poor indicator of renal function.
    • Causes of Reduced Creatinine

    • Low muscle mass - women, children, the elderly, malnourished patients, cancer patients
    • Muscle wasting
    • Low protein intake - low protein diet, malnutrition, malabsorption, alcoholism
 
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 Bellomo R, Kellum JA, Ronco C. Acute kidney injury. The Lancet. 2012 Aug 31;380(9843):756-66.
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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.
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.
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