Creatinine - Definition

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Creatinine is a substance derived from the degradation of creatine in the muscle cells. It is actually just simple organic waste, which would normally be eliminated in the urine after passing through the kidneys. It is nevertheless very useful in medicine to assess the elimination performed by the renal glomeruli. The GFR or glomerular filtration rate is estimated by calculating the creatinine clearance based on creatinine levels in the blood (serum creatinine), but also the age, sex, and weight of the individual. Two formulas are commonly used, the Cockcroft and the MDRD, which is more reliable in certain cases especially among the elderly. The creatinine clearance enables the identification of kidney failure.