Usefulness and limitations of neutrophil gelatinase-associated lipocalin in the assessment of kidney diseases

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25 kDa glycoprotein expressed and secreted by renal tubular cells, immune cells and cancer cells under various pathologic states. NGAL plays important roles in renal tubular epithelial recovery, bacterial defense and inflammation. Currently, NGAL is considered as an accurate early biomarker for acute renal disease, and also shows great potential in improving the assessment of risk groups and the short-term and the long-term prognosis of chronic renal disease. Systemic reviews and meta-analysis illustrated that systemic and urinary NGAL have similar sensitivity and specificity for assessing renal damage, however, emerging studies found that they behaved dissimilar in certain patients, suggesting they may have different clinical significances. Moreover, plenty of studies have found that pathologic conditions, like inflammation, sepsis and cancer also upregulate NGAL protein, which caused the fluctuations of systemic and urinary NGAL concentrations and blurred the accuracy of NGAL as renal damage indicator. The purpose of this review article is to examine the different performances of systemic and urinary NGAL in diagnosis and prognosis of renal diseases and summarize the current knowledge on factors affecting NGAL as sensitive renal damage biomarker.