CST4 and acute kidney injury: This is in contrast to all other established AKI-specific biomarkers such as the NephroCheck parameters TIMP2 and IGFBP7 [9,10], neprilysin [5], NGAL [6], cystatin [7], KIM1 [4] and IL18 [8], which increase during AKI due to cell lesion or cell membrane injury.