NEUTROPHIL GELATINASE-ASSOCIATED LIPOCALIN [NGAL] AS A DIAGNOSTIC AND PROGNOSTIC BIOMARKER

Neutrophil gelatinase-associated lipocalin (NGAL), also known as lipocalin-2 or siderocalin, is a 25-kDa protein of the lipocalin superfamily that was first isolated from human neutrophil granules and subsequently identified as one of the most highly and rapidly induced genes in the kidney following ischaemic and nephrotoxic injury.[4, 5] Over the past two decades, NGAL has emerged as one of the most extensively studied biomarkers in clinical medicine, with a diagnostic footprint that extends well beyond its original description as an early indicator of acute kidney injury (AKI). This review synthesises current evidence on the biology, physiological regulation, and diagnostic performance of NGAL across a range of clinical contexts, including cardiac-surgery-associated AKI, sepsis and critical illness, contrast-induced nephropathy, chronic kidney disease, cardiovascular disease, urinary tract infection, and malignancy. Particular attention is given to the analytical characteristics of NGAL assays, including point-of-care platforms, and to the confounding factors that limit its specificity, most notably systemic inflammation and pre-existing renal impairment. While NGAL consistently outperforms serum creatinine in the early detection of tubular injury, with pooled sensitivities and specificities in the range of 70-90% across multiple meta-analyses, its diagnostic accuracy is heterogeneous across clinical settings and is influenced by the timing of sampling, the specimen matrix used (serum, plasma, or urine), and the presence of concurrent inflammatory states. This review concludes that NGAL holds substantial value as an adjunctive diagnostic and prognostic biomarker, particularly when used within defined clinical contexts and in combination with other markers of kidney injury, but that its role as a stand-alone diagnostic test remains constrained by its lack of organ specificity.