Method: A cross - sectional prospective study was performed over 130 patinets with renal diseases in nephrology department - Cho Ray hopital from 12/2009 to 8/2010 having serum creatinine 0.8 - 3.0mg / dL, serum cystatin C is determined by test Latex turbidimetry, the 24h creatinine clearance correcting with BSA (as the standard to compare with others), and the predicted creatinine clearance of Cockcroft-Gault.