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:

• `v_u` = volumetric flow rate of urine
• U_"PAH" - the urine concentration of para-aminohuippurate in the urine sample
• P_"PAH" - the plasma concentration of para-aminohuippurate in the blood samplesample

Notes

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.