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The normal range of GFR, adjusted for body surface area, is 100–130 average 125 mL/min/1.73m 2 in men and 90–120 ml/min/1.73m 2 in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 mL/min/1.73 m 2 until 2 years of age in both sexes, and then it progressively decreases.
There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR). The above formula only applies for GFR calculation when it is equal to the clearance rate. The normal range of GFR, adjusted for body surface area, is 100–130 average 125 (mL/min)/(1.73 m 2) in men and 90–120 (mL/min)/(1.73 m 2 ...
This is the numerator in the equation. The denominator is the total amount of sodium filtered by the kidneys. This is calculated by multiplying the plasma sodium concentration by the glomerular filtration rate (GFR) calculated using creatinine filtration. The flow rates then cancel out, simplifying to the standard equation: [1]
Typically, in an adult human, the net filtration pressure is 10mmHg and Kf 12.5mL/min/mmHg, giving a glomerular filtration rate (GFR) of 125mL/min. A decrease in Kf due to reduced number of glomeruli or reduced permeability will reduce the GFR at a given filtration pressure [ 3 ]
Algorithms to estimate GFR from creatinine concentration and other parameters are discussed in the renal function article. Unfortunately, the MDRD Study equation was developed in people with chronic kidney disease, and its major limitations are imprecision and systematic underestimation of measured GFR (bias) at higher/normal values. [20]
GFR on its own is the most common and important measure of renal function. However, in conditions such as renal artery stenosis, blood flow to the kidneys is reduced. Filtration fraction must therefore be increased in order to perform the normal functions of the kidney. Loop diuretics and thiazide diuretics decrease filtration fraction.
Para-aminohippurate (PAH) clearance is a method used in renal physiology to measure renal plasma flow, which is a measure of renal function. [citation needed]PAH is completely removed from blood that passes through the kidneys (PAH undergoes both glomerular filtration and tubular secretion), and therefore the rate at which the kidneys can clear PAH from the blood reflects total renal plasma flow.
When the substance "C" is creatinine, an endogenous chemical that is excreted only by filtration, the clearance is an approximation of the glomerular filtration rate. Inulin clearance is less commonly used to precisely determine glomerular filtration rate. Note - the above equation is valid only for the steady-state condition.
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