The renal function disorder may develops without symptoms and can damage the kidney up to 70-80%. The glomerular filtration rate is one of the most useful parameters of renal function available and is most accurately measured by insulin clearance. Since Creatinin is an imperfect filtration marker, alternative clearance techniques have been developed. Inulin clearance is the gold standard for assessing glomerular filtration rate (GFR). It is considered is impractical and particularly inconvenient for patients. Cystatin is an endogenous marker of renal function, a low molecular mass protein. Cystatin C is produced at a constant rate by all nucleated cells. The production rate of cystatin C is unaltered by gender, age, body mass, food intake, drugs inflammatory condition and cancer. So, it can be used as a good marker to assess the renal function of the patient with penyakit hati, anorectic, and neuromuscular disesase. Serum is 3% higher than the plasma. Cystatin C production in the body is a stable process that is not influenced by hemoglobin, bilirubin, trigliserid, rematoid factors and paraprotein at certain level.