PAH clearance

PAH clearance
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

Para aminohippurate clearance or PAH clearance is a method used in renal physiology to measure renal plasma flow, which, in turn, is a measure of renal function.

The concentration of para aminohippurate (PAH) is measured in one arterial blood sample (PPAH) and one urine sample(UPAH). The urine flow (V) as also measured. Renal perfusion flow is then calculated by:

RPF = \frac{U_{PAH}}{P_{PAH}} V

What in fact is calculated is the effective renal plasma flow (eRPF). However, since the renal extraction ratio of PAH almost equals 1, then eRPF almost equals RPF.


The renal extraction ratio of PAH in a normal individual is approximately 0.92[1], and thus not exactly 1.0. Thus, this method usually underestimates RPF by approximately 10%. This margin of error is generally acceptable considering the ease with which eRPF is measured.


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