Laboratory Measurement
Renal expression of NGAL increases in the kidneys after injury for a variety of reasons. The level of NGAL in the urine and plasma increases within 2 hours of kidney injury. It is possible to measure NGAL in serum or urine in the range of 25 to 5,000 ng/mL by current laboratory tests. Low levels for NGAL have been considered to be 20 ng/mL, medium levels 200 ng/mL, and high levels 1200 ng/mL.
A study on children with pediatric cardiopulmonary bypass operations showed that urinary NGAL concentrations above 50 ng/mL 2 hours after surgery is indicative of serum creatinine levels 50% over basal values. Normally, children tend to have almost undetectable levels of NGAL. Therefore, studies that include children are considered to be “pure.” Adult patients presenting for cardiopulmonary bypass surgery are not considered to be “pure” in NGAL studies because adults often have other disorders such as inflammatory conditions, which can cause slight increases in NGAL.
AKI studies investigating the use of NGAL as a biomarker often compare serum creatinine and NGAL production. Unfortunately, serum creatinine production is variable; therefore, the comparison is not always reliable. In addition, NGAL levels are relative to each person, and a study on specific numbers and their accurate predicted outcomes is yet to be done.
Although NGAL is generally a precise biomarker of AKI, there are limitations to the use of the biomarker. Studies have proven that NGAL is not only present when there is chance for AKI. There are many other ways to have elevated NGAL levels such as taking certain kinds of antibiotics and other endogenous substances. Creatinine, for example, can elevate NGAL levels and create a false positive for an AKI. There are also some medical conditions that may interfere with NGAL levels including Epstein-Barr Virus, Hepatitis A Virus, Herpes Simplex Virus, Myeloma, and Rubella Virus.
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