Renal GFR is best measured by –

Inulin clearance is the gold standard for assessing GFR. It is the preferred measure of GFR when an accurate measure is critical. However, this method is not performed in clinical practice, because of technical complexity and limited availability. Next to inulin, radiocontrast agents (Tc - DTPA) are most accurate. However, because of its convenience and low cost, creatinine clearance is most commonly used.