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Extraction ratio is a measure in renal physiology, primarily used to calculate renal plasma flow in order to evaluate renal function. It is the amount of compound entering the kidney that got excreted into the final urine.〔(Renal Mathematics ) Texas Tech University Health Sciences Center〕 Measured in concentration in blood plasma, it may thus be expressed as: : , where Pa is the concentration in renal artery, and Pv is the concentration in the renal vein. For instance, para aminohippuric acid (PAH) is almost completely excreted in the final urine, and thus almost none is found in the venous return (Pv ~0). Therefore, the extraction ratio of PAH ~1. This is why PAH is used in PAH clearance to estimate renal plasma flow. Hepatic Extraction Ratio is a similar measurement for clearance of a substance(usually a pharmacological drug) by the liver. defined as fraction of drug removed from blood by the liver. it depends on 3 factors, the hepatic blood flow, the uptake into the (), and the enzyme metabolic capacity. examples of drugs with a high hepatic extaction ratio include () () and () ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「extraction ratio」の詳細全文を読む スポンサード リンク
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