Correlation of NGAL serum levels. (a and c). Correlation of NGAL serum levels with sepsis and acute kidney injury (AKI). Bar charts (mean ± standard error of the mean) showing serum neutrophil gelatinase-associated lipocalin (NGAL) levels of critically ill patients with AKI at inception of renal replacement therapy (RRT) stratified by (a) the presence (n = 31) or absence (n = 78) of sepsis as according to the SCCM/ESICM/ACCP/ATS/SIS International Sepsis Definitions , or (c) stratified by the renal variable from the Sequential Organ Failure Assessment (SOFA) score (1 point (n = 9), 2 points (n = 27), 3 points (n = 28), 4 points (n = 45)). (b and d) Scatter plot showing the correlation of serum NGAL concentrations with (c) C reactive protein (CRP) levels, and (d) serum cystatin C levels in critically ill patients at initiation of RRT (n = 109).