Although post-op renal function decrease is determined by serum creatinine, serum creatinine has disadvantages that it increases a long time after renal function decrease and it has various increasing time based on the level of renal function. Neutrophil Gelatinase-associated Lipocalin (NGAL's) usefulness as an evidence for acute kidney damage occurring from post-op cardiac surgery, being critical patients and contrast medium use is already proven.