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
			ER=90%
			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 (P_PAH) and one urine sample(U_PAH). 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.

Precision

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.

References

1. ^ Reubi FC (September 1953). "Glomerular filtration rate, renal blood flow and blood viscosity during and after diabetic coma" (PDF). Circulation Res. 1 (5): 410–3. PMID 13082682. http://circres.ahajournals.org/cgi/reprint/1/5/410.pdf.