In the search for diagnostic and prognostic markers of AKI, numerous markers of renal cellular damage have been identified [8,9,10]; these include neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18), liver-type fatty acid-binding protein (L-FABP), tissue inhibitor of metalloproteinases type 2 (TIMP-2), insulin-like growth factor-binding protein 7 (IGFBP7), kidney injury molecule-1 (KIM-1) and proenkephalin (PENK). Here, PENK is linked to acute kidney injury.