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.
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.