Abstract
Despite its name, the current diagnosis of acute kidney injury (AKI) still depends on markers of decreased kidney function and not on markers of injury. This results in a delayed diagnosis: AKI is diagnosed based on serum creatinine criteria only when the severity of injury is enough to decrease glomerular filtration rate. Moreover, by the time AKI is diagnosed, the insult may have already ceased, and even appropriate therapy targeted at the specific insult and its associated pathogenic pathways may no longer be effective. Biomarkers of injury are needed that allow the diagnosis of AKI based on injury criteria. At least three commercially available immunoassays assessing urinary or plasma neutrophil gelatinase-associated lipocalin and urinary tissue inhibitor of metalloproteinases-2 × insulin-like growth factor-binding protein-7 ([TIMP2]*[IGFBP7]) (NephroCheck(®)) have generated promising data regarding prediction and early diagnosis of AKI, although their relative performance may depend on clinical context. Recently, a urinary peptidomics classifier (PeptAKI) was reported to predict AKI better than current biomarkers. Focusing on [TIMP2]*[IGFBP7], the cellular origin of urinary TIMP2 and IGFBP7 remains unclear, especially under the most common predisposing condition for AKI, i.e. chronic kidney disease. We now discuss novel data on the kidney cell expression of TIMP2 and IGFBP7 and its clinical implications.