Lipocalin-2 (LCN2), also known as oncogene 24p3 or neutrophil gelatinase-associated lipocalin (NGAL), is a protein that in humans is encoded by the LCN2 gene. NGAL is involved in innate immunity by sequestering iron and preventing its use by bacteria, thus limiting their growth. It is expressed in neutrophils and in low levels in the kidney, prostate, and epithelia of the respiratory and alimentary tracts. NGAL is used as a biomarker of kidney injury. Function The binding of NGAL to bacterial siderophores is important in the innate immune response to bacterial infection. Upon encountering invading bacteria, the toll-like receptors on immune cells stimulate the synthesis and secretion of NGAL. Secreted NGAL then limits bacterial growth by sequestering iron-containing siderophores. Lipocalin-2 binds, next to bacterial siderophores, also to the mammalian siderophore 2,5-dihydroxybenzoic acid (2,5-DHBA). This complex ensures that excess free iron does not accumulate in the cytoplasm. Mammalian cells lacking 2,5-DHBA accumulate abnormal intracellular levels of iron leading to high levels of reactive oxygen species. Lipocalin-2 also functions as a growth factor and participates in synaptic plasticity. Clinical significance In the case of acute kidney injury (AKI), NGAL is secreted in high levels into the blood and urine within 2 hours of injury. Because NGAL is protease resistant and small, the protein is easily excreted and detected in the urine. NGAL levels in patients with AKI have been associated with the severity of their prognosis and can be used as a biomarker for AKI NGAL can also be used as an early diagnosis for procedures such as chronic kidney disease, contrast induced nephropathy, and kidney transplant. Kidney health is most frequently measured by serum creatinine. Serum creatinine is a marker of kidney function, whereas NGAL is a marker of kidney injury. NGAL levels are a more precise and sensitive marker for diagnosing AKI than serum creatinine levels. Therefore, monitoring NGAL levels reduces delayed AKI diagnosis and treatment. Using a more sensitive and specific marker allows for earlier diagnosis, correct responses to AKI, and reduced risk of morbidity and mortality. The NGAL level measured in an individual is proportional to the severity of the AKI. Individuals positive for NGAL tend to have higher incidence of renal replacement therapy and have higher rates of in-hospital mortality, both in the presence and the absence of serum creatinine. Therefore, an individual may have AKI without the presence of serum creatinine. The ability to diagnose AKI before