Creatinine (from the Greek kreas , flesh) is a break-down product of creatine phosphate in muscle , and is usually produced at a fairly constant rate by the body (depending on muscle mass).

Creatinine is chiefly filtered by the kidney, though a small amount is actively secreted. more

Creatinine (from the Greek kreas , flesh) is a break-down product of creatine phosphate in muscle , and is usually produced at a fairly constant rate by the body (depending on muscle mass).

Creatinine is chiefly filtered by the kidney, though a small amount is actively secreted. There is little-to-no tubular reabsorption of creatinine. If the filtering of the kidney is deficient, blood levels rise. As a result, creatinine levels in blood and urine may be used to calculate the creatinine clearance (CrCl), which reflects the glomerular filtration rate (GFR). The GFR is clinically important because it is a measurement of renal function. However, in cases of severe renal dysfunction, the creatinine clearance rate will be "overestimated" because the active secretion of creatinine will account for a larger fraction of the total creatinine cleared. Ketoacids , cimetidine and trimethoprim reduce creatinine tubular secretion and therefore increase the accuracy of the GFR estimate, particularly in severe renal dysfunction. (In the absence of secretion, creatinine behaves like inulin .) less