effective renal plasma flow effective renal plasma flow effective renal plasma flow (erpf) is a measure used in renal physiology 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.: 664–665 the actual rpf can be calculated from erpf as follows: actual rpf = erpf extraction ratio = where extraction ratio is the ratio of compound entering the kidney that is excreted into the final urine.: 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.