NGAL (neutrophil gelatinase-associated lipocalin) is an acute phase protein, participating in antibacterial immunity. NGAL forms a complex with metalloproteinase 9 (MMP-9), thereby increasing its activity and preventing its degradation. NGAL is freely filtered through the glomerular membrane and reabsorbed by endocytosis in the proximal tubule. NGAL detected in urine is produced mainly in the distal nephron. Elevated serum and urine NGAL allows diagnosis of acute kidney injury approximately 24 hours earlier than plasma creatinine concentration. Increased levels of NGAL were detected in patients with acute myocardial infarction, heart failure or stroke and were demonstrated to be strong predictors of adverse prognosis.