What is the formula for calculating the filtration fraction (FF)?

The filtration fraction (FF) is a crucial parameter in renal physiology that represents the proportion of plasma that is filtered through the glomeruli into the Bowman's capsule. It is calculated using the formula FF = GFR / RPF, where GFR stands for Glomerular Filtration Rate, and RPF stands for Renal Plasma Flow.

The rationale behind this calculation is that GFR quantifies the volume of plasma that is filtered per unit time, while RPF quantifies the total volume of plasma that passes through the kidneys in that same timeframe. By dividing GFR by RPF, we can ascertain what fraction of the renal plasma flow is actually being filtered into the renal tubules as urine. This ratio helps in understanding kidney function and can be impacted by various physiological conditions, including dehydration, renal artery stenosis, and others.

This understanding is vital in clinical settings where kidney function is a concern, providing insight into the efficiency of renal filtration and overall kidney health. The other provided formulae do not correctly represent the relationship between GFR and RPF as it pertains to the calculation of filtration fraction.