Serum and urinary biomarkers of acute kidney injury

Acute kidney injury (AKI) is a frequent clinical problem in critically ill patients and the associated mortality is high. Standard serum and urine biomarkers are insensitive and nonspecific for the detection of kidney injury in its early stages which limits the therapeutic options and may compromise the outcome. The study presents new candidates for biochemical markers of AKI, with potentially high sensitivity and specificity, causally related to its pathogenesis and development. Some of these biomarkers measured in serum or urine are well known in laboratory practice but have been used in other tests, while some novel biomarkers have been proposed as a result of experimental and clinical studies. In current clinical practice, identification and classification of AKI is based on elevations in serial serum creatinine concentrations, which are delayed and therefore unreliable in the acute setting. The most promising of the new serum AKI markers are cystatin C, neutrophil gelatinase-associated lipocalin and uric acid. Urinary AKI markers may be classified as enzymes released from damaged tubular cells (alkaline phosphatase, gamma-glutamyl transpeptidase, alanine aminopeptidase, isoenzymes of glutathione transferase, N-acetyl-beta-D-glucosaminidase), low-molecular-weight proteins (alpha(1)-microglobulin, beta(2)-microglobulin, retinol-binding protein, cystatin C) and proteins specifically produced in the kidney and associated with the development of AKI [cysteine-rich protein 61, neutrophil gelatinase-associated lipocalin, kidney injury molecule 1, cytokines and chemokines (Gro-alpha, IL-18), and structural and functional proteins of renal tubules (F-actin, Na(+)/H(+) exchange isoform 3)]. Based on the different expression of these markers, using a panel of serum and urine markers may potentially help to distinguish between various types of insults, establish the duration and severity of injury, predict the clinical outcome and help to monitor response to treatment in AKI.