Test Details: The best overall indicator of the glomerular function is the glomerular filtration rate (GFR). GFR is the rate in milliliters per minute at which substances in plasma are filtered through the glomerulus; in other words, the clearance of a substance from the blood. The most commonly used endogenous marker for the assessment of glomerular function is creatinine. Glomerular filtration rate (GFR) test is done to diagnose and monitor treatment of acute and chronic renal diseases, to adjust dosage of renally excreted medications and to monitor renal transplant recipients.