PENK and acute kidney injury: According to the AKI continuum, biomarkers can be broadlyclassified into two main categories: damage markers and dysfunction markers, suchas human neutrophil gelatinase-associated lipocalin (NGAL), KIM-1, liver-type fatty acid–binding protein (L-FABP) and C-C motifchemokine ligand 14 (CCL14) as damage markers; proenkephalin amino acids 119through 159 (penKid) as a function marker, and as stress tissue inhibitor ofmetalloproteinases-2 (TIMP2) and insulin-like growth factor–binding protein 7(IGFBP7) [126].