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Extraction ratio

Parameter Value
renal blood flow RBF=1000 ml/min
hematocrit HCT=40%
renal plasma flow RPF=600 ml/min
filtration fraction FF=20%
glomerular filtration rate GFR=120 ml/min
urine flow rate V=1 mL/min
Sodium Inulin Creatinine PAH
SNa=150 mEq/L SIn=1 mg/mL SCr=0.01 mg/ml SPAH=
UNa=710 mEq/L UIn=150 mg/mL UCr=1.25 mg/mL UPAH=
CNa=5 mL/min CIn=150 ml/min CCr=125 mL/min CPAH=420 ml/min
ERPF=540 ml/min

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.[1]

Measured in concentration in blood plasma, it may thus be expressed as:

<math>Extraction ratio = \frac{P_a - P_v}{P_a}</math>

, 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 ration of PAH ~1. This is why PAH is used in PAH clearance to estimate renal plasma flow.


  1. ^ Renal Mathematics Texas Tech University Health Sciences Center