Cystatin C is a comparatively small protein that is produced throughout the body by all nucleated cells and is found in a variety of body fluids, including the blood. It is filtered from the blood by the kidneys and broken down at a constant rate. This test measures the amount of cystatin C in blood to help evaluate kidney function. Its an alternative for creatinine and creatinine clearance tests. Use serum, EDTA /Heparin plasma as specimen