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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.
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}}}}
Upon presentation of decreased renal function, it is recommended to perform a history and physical examination, as well as performing a renal ultrasound and a urinalysis. [ citation needed ] The most relevant items in the history are medications , edema , nocturia , gross hematuria , family history of kidney disease, diabetes and polyuria .
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.
Therefore, the urinary and plasma concentrations of sodium must be compared to get an accurate picture of kidney clearance. In clinical use, the fractional excretion of sodium can be calculated as part of the evaluation of acute kidney failure in order to determine if hypovolemia or decreased effective circulating plasma volume is a contributor ...
Extraction ratio is a measure in renal physiology, primarily used to calculate renal plasma flow in order to evaluate renal function. It measures the percentage of the compound entering the kidney that was excreted into the final urine. [1] Measured in concentration in blood plasma, it may thus be expressed as:
Measurement of renal or plasma clearance of 51 Cr-EDTA is widely used in Europe but not available in the United States, where 99m Tc-DTPA may be used instead. [10] Renal and plasma clearance 51 Cr-EDTA has been shown to be accurate in comparison with the gold standard, inulin.
Clearance is therefore expressed as the plasma volume totally free of the drug per unit of time, and it is measured in units of volume per units of time. Clearance can be determined on an overall, organism level («systemic clearance») or at an organ level (hepatic clearance, renal clearance etc.). The equation that describes this concept is: