Answer: GFR is glomerular filtration rate. It is the measure used to identify people with kidney disease. About 20 million people in USA have some kind of chronic kidney disease many of whom have end stage kidney disease. The GFR helps to identify early kidney disease and thus helping to reduce progression to more advanced kidney disease. The gold standard of measuring kidney function is through measuring the clearance of inulin but this is not practical. A more practical but not convenient way is to measure creatinine clearance in 24 hours urine collection. Creatinine is formed by break of muscles and is mostly filtered and to a lesser extent secreted by the kidney. Its endogenous production decreases in elderly and its secretion is affected by diabetes, medications such as trimethoprim and cimitidine without affecting GFR. Many online formulas are used to calculate an estimate of GFR based on age and creatinine.