What is the equation for glomerular filtration rate (GFR)?

The equation for glomerular filtration rate (GFR) is fundamentally derived from the principles of clearance and renal function. The correct equation, GFR = U inulin x (V / P inulin), accurately reflects the calculation of how efficiently inulin, a substance freely filtered at the glomerulus and not secreted or reabsorbed, is cleared from the blood by the kidneys.

In this equation, "U inulin" represents the concentration of inulin in the urine, "V" stands for the urine flow rate (the volume of urine produced per unit time), and "P inulin" indicates the concentration of inulin in the plasma. When you multiply the urine concentration (U inulin) by the urine flow rate (V) and then divide by the plasma concentration (P inulin), the equation provides a measure of the volume of plasma that is filtered by the kidneys per unit time, which is the definition of GFR.

This method of measuring GFR is highly reliable because inulin is not reabsorbed or secreted by the renal tubules, thus allowing for a clear estimation of the filtration capability of the kidneys without interference from other processes.

The equation captures the essential relationship between these variables and is foundational in