Neutrophil Gelatinase-Associated Lipocalin, or NGAL, is a protein detected in urine. While normally present at low levels in the body, its concentration in urine can provide information about a person’s health.
Understanding NGAL
NGAL is a small, secreted glycoprotein that belongs to the lipocalin family of proteins. These proteins are known for their ability to transport small, hydrophobic substances within the body. NGAL is primarily secreted by immune cells like neutrophils, macrophages, and dendritic cells, but it is also expressed in various human tissues, including the kidneys, heart, lungs, and liver.
Under normal physiological conditions, NGAL plays a part in immune responses and cell growth. For instance, it can help protect against bacterial infections by sequestering iron, a nutrient vital for bacterial growth. NGAL also helps regulate iron-responsive genes and can stabilize certain proteolytic enzymes. Healthy individuals typically have low levels of NGAL in their plasma, averaging around 72 ng/ml, with a range of 40–109 ng/ml.
NGAL as a Kidney Health Marker
NGAL is measured in urine because its levels increase rapidly when the kidneys experience injury. It is an early marker for kidney damage, particularly in Acute Kidney Injury (AKI). Kidney damage leads to increased NGAL synthesis in the distal nephron and decreased reabsorption by the proximal tubules, resulting in a substantial rise in urine NGAL levels.
NGAL is a sensitive measure of renal tubular injury. Unlike older markers like serum creatinine, which often change only after significant kidney damage, NGAL levels can rise within 24–72 hours after injury, potentially predicting AKI days earlier. This early detection allows for more timely interventions, helping prevent severe and irreversible kidney damage.
Interpreting Urine NGAL Levels
Elevated NGAL levels in urine can signal kidney stress or damage, often associated with various types and stages of kidney injury. NGAL can help differentiate between AKI subtypes, such as acute tubular necrosis, hepatorenal syndrome, and pre-renal azotemia. While high levels suggest kidney issues, they do not provide a definitive diagnosis on their own.
A urine NGAL level below 149 ng/ml is considered low risk for AKI, but it does not completely rule out future development. Levels between 150-300 ng/ml suggest a moderate risk, while concentrations exceeding 300 ng/ml indicate a high risk for kidney injury. These interpretations are used in conjunction with a patient’s medical history, other laboratory tests, and clinical presentation, as NGAL elevations can also occur due to non-renal conditions like infections, inflammation, or certain cancers.
The Urine NGAL Test
A urine NGAL test typically involves providing a random urine sample, with a clean-catch method preferred to minimize contamination. Using the first morning urine is often recommended. The collected sample should ideally be tested within 24 hours, but it can be refrigerated for up to three days or frozen for longer storage, preferably at -20°C or below.
Once the sample reaches the laboratory, it is usually processed within a few hours, with results often available within 24 hours. The test is performed in hospitals or specialized laboratories using immunoassay methods. These tests quantify the NGAL protein, aiding clinicians in assessing kidney health.