CST3 and acute kidney injury: Serum cystatin C (CysC) is a low molecular weight proteinase produced by all nucleated cells and is easily filtrated by the glomerulus and reabsorbed in the proximal tubular cells [30]; it is a marker for glomerular filtration function, rather than a diagnosis tool for AKI, and has been recognized by the FDA since 2002 [31,32].