Effective renal plasma flow

"eRPF" redirects here. For the river in Baden-Württemberg, Germany, see Erpf (river).

Effective renal plasma flow (eRPF) is a measure used in renal physiology^[1] to calculate renal plasma flow (RPF) and hence estimate renal function.

Parameter	Value
renal blood flow	RBF = 1000 mL/min
hematocrit	HCT = 40%
glomerular filtration rate	GFR = 120 mL/min
renal plasma flow	RPF = 600 mL/min
filtration fraction	FF = 20%
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

Because the extraction ratio of PAH is high, it has become commonplace to estimate the RPF by dividing the amount of PAH in the urine by the plasma PAH level, ignoring the level in renal venous blood. The value obtained in this way is called the effective renal plasma flow (eRPF) to indicate that the level in renal venous plasma was not measured.^{[2]: 664–665}

The actual RPF can be calculated from eRPF as follows:

${\displaystyle {\text{Actual RPF}}={\frac {\text{eRPF}}{\text{Extraction ratio}}}}$

where extraction ratio is the ratio of compound entering the kidney that is excreted into the final urine.^{[2]: 664–665}

When using a compound with an extraction ratio near 1, such as para-aminohippurate (PAH), eRPF approximates RPF. Therefore, PAH clearance can be used to estimate RPF.^[3]