It was observed that patients who developed Acute Kidney Injury (AKI) showed a significant increase in proenkephalin levels in the plasma, reaching 145.0 pmol/l for septic AKI, with a sensitivity of 67.9% and specificity of 98.3%, and an area under the curve (AUC) of 0.796 [93]. Here, PENK is linked to acute kidney injury.