Explain the Inulin Clearance Test

Inulin is a complex polysaccharide found in specific plant roots. In the test, a fixed amount of inulin is infused into the blood at a constant rate. The inulin is filterable, that is, it passes freely through the glomerular membranes that are why its concentration in the glomerular filtrate equivalent that of the plasma. In the renal tubule, inulin is not reabsorbed to any significant degree nor is it secreted by the tubules. It does not modify the renal function and is easily estimable. Consequently, the rate at which it appears in the urine can be used to calculate the rate of glomerular filtration. Inulin clearance can be calculated from the following formula,