Chronic renal failure is defined as gradual deterioration of glomerular filtration rate.. It can occur over a period of time,which can vary from months to years. The severity of renal failure is assessed by the amount of reduction in glomerular filtration rate. The glomerulat filtration rate (GFR) is usually calculated by using the the creatinine levels of the body. It is calculated by using the following formula.
GFR = {1.23 * [140 - age (years)] * weight (Kg) }/ plasma creatinine (micro mol/l)
Creatinine is released in to the plasma by muscles. The amount of creatinine released in to the circulation is fairly constant. These creatinine molecules are excreted from the body by the kidneys. Most of them are filtered through the glumeruli and a small amount is secreted from the renal tubules. In chronic kidney disease, when the renal tubules get damaged, the amount of creatinine secreted from the renal tubules can increase. As a result, more creatinine is excreted from the body. Ultimately the plasma creatinine levels reduces despite of existing renal damage. So, the GFR increases when calculated from the above formula.
Therefore, there should be a more accurate method to calculate GFR. It is done by measuring the clearance of radioactive EDTA or lohexol, a non ionic contrast medium.
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