Glomerular filtration rate is a direct measure of renal function, starting to decline early in the course of renal disease. Accurate determination of GFR is required for monitoring the progression of renal disease, and when deciding on therapy to avoid impairing the organ function.

Ideally, GFR is measured by clearance of a biologically inert substance freely filtered through the glomerular membrane and not re-entering circulation. Several commonly accepted true filtration markers of exogenous clearance methods are available, such as inulin and radiolabeled solutes. However, their routine use is limited for technical, economical and organisational reasons.