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The renal clearance ratio or fractional excretion is a relative measure of the speed at which a constituent of urine passes through the kidneys. [ 1 ] [ 2 ] It is defined by following equation: c l e a r a n c e r a t i o o f X = C x C i n {\displaystyle clearance\ ratio\ of\ X={\frac {C_{x}}{C_{in}}}}
Creatinine clearance exceeds GFR due to creatinine secretion, [4] which can be blocked by cimetidine. Both GFR and C Cr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result ( eGFR and eC Cr ) The results of these tests are used to assess the ...
Thus, total body clearance is equal to the sum clearance of the substance by each organ (e.g., renal clearance + hepatic clearance + pulmonary clearance = total body clearance). For many drugs, however, clearance is solely a function of renal excretion. In these cases, clearance is almost synonymous with renal clearance or renal plasma clearance.
Therefore, creatinine concentrations in blood and urine may be used to calculate the creatinine clearance (CrCl), which correlates approximately with the glomerular filtration rate (GFR). Blood creatinine concentrations may also be used alone to calculate the estimated GFR (eGFR). The GFR is clinically important as a measurement of kidney function.
The glomerular filtration rate is the flow rate of filtered fluid through the kidney. The creatinine clearance rate (C Cr or CrCl) is the volume of blood plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. Creatinine clearance exceeds GFR due to creatinine secretion, [1] which can be blocked by ...
Fractional excretion of other substances can be measured to determine kidney clearance including urea, uric acid, and lithium. These can be used in patients undergoing diuretic therapy, since diuretics induce a natriuresis. Thus, the urinary sodium concentration and FE Na may be higher in patients receiving diuretics in spite of prerenal ...
where C is the concentration [mol/m 3]; t is the time [s]; K is the clearance [m 3 /s]; V is the volume of distribution [m 3]; From the above definitions it follows that is the first derivative of concentration with respect to time, i.e. the change in concentration with time.
The "Hepatic Extraction Ratio" is a similar measurement for clearance of a substance (usually a pharmacological drug) by the liver. It is defined as the fraction of drug removed from blood by the liver, and depends on 3 factors— the hepatic blood flow, the uptake into the hepatocytes, and the enzyme metabolic capacity.