HLA-G and acute kidney injury: Generally speaking, the biomarkers of AKI are categorized into three groups, namely, functional biomarkers (such as SCr, cystatin C, α1- or β2-microglobulin), tubular enzymes (such as α-glutathione-S-transferase (α-GST)), and unregulated proteins (such as NGAL, L-type fatty acid-binding protein (L-FABP), kidney injury molecule-1 (KIM-1) and IL-18) [117].