This equation computes the renal plasma flow from the measurements taken of urine flow rate and the concentration of a specific substance, para-aminohuippurate, introduced into the bloodstream.
Inputs to this equation are:
DERIVING THE GFR EQUATION
The mass of the substance excreted during the time urine is collected defines the concentration of the substance introduced into the blood, the para-aminohuippurate (PAH), in the urine, `U_"PAH"`. This concentration in the urine can be compared to the plasma concentration, `P_"PAH"` of the same substance introduced into the blood and to the volume flow of urine, `V_U`. From the ratios of these measurements we can derive the estimate of the volumetric flow of plasma that was filtered, thus the GFR.