*2.2. Plasma and Serum Damage Markers*

Damage markers can help in early AKI diagnosis even before elevation of sCr and sCyst-C levels [5]. Only a few damage markers are measured in serum or plasma: NGAL, KIM-1, osteopontin and netrin-1. The most studies concerned changes in NGAL.

NGAL, also known as siderocalin or lipocalin 2, is a member of the lipocalin superfamily of carrier proteins, which are approximately 25 kDa in size. NGAL has a bacteriostatic function related to its ability to bind iron-siderophore complexes and thereby prevents iron uptake by bacteria. NGAL also provides an antiapoptotic effect and enhances proliferation of renal tubular cells [8]. It is produced by activated neutrophils in the proximal tubules. NGAL is filtered in the glomerulus and reabsorbed in the proximal tubule. After ischemic, septic or toxic kidney injury, NGAL is dramatically upregulated at the transcript and protein level. Plasma and urinary NGAL levels are significantly increased in those with early structural renal tubular damage caused by various factors [5,8,9].
