Urinary neutrophil gelatinase-associated lipocalin (uNGAL) is highly sensitive and specific for diagnosing urinary tract infections (UTIs), according to a study in febrile children aged up to 24 months. A protein found in the collecting duct of the kidney, uNGAL inhibits bacterial growth, and previous research has shown that it is significantly elevated with Gram-negative UTIs.
The study was conducted in 260 patients who were evaluated in a pediatric emergency department for UTIs using uNGAL levels, urinalysis (UA), Gram stain, and culture. Of this total, 35 had UTIs (32 were caused by Gram-negative organisms), of whom 22 had definite UTIs and 13 possible UTIs. The median uNGAL level was 215.1 ng/mL in those diagnosed with a UTI and 4.4 ng/mL in those without the infection. Median uNGAL levels were successively higher in those with no UTI, a possible UTI, and a definite UTI.
Using a threshold value of 39.1 ng/mL, uNGAL sensitivity was 97.1% and specificity 95.6%. A comparison of uNGAL with UA and Gram stain found that uNGAL had higher sensitivity than UA (using leukocyte esterase-nitrite) with similar specificity. Gram-stain had a somewhat lower sensitivity than uNGAL but with high specificity (Lubell TR, et al. Pediatrics. 2017;140:e20171090).
Thoughts from Dr. Burke
As UTI is a common, treatable, potentially serious cause of fever in children, I am always on the lookout for better ways to make an early, accurate diagnosis. Urinary NGAL may prove to be the next best thing. Unlike leukocyte esterase, this assay does not require the presence of white blood cells in the urine. It has excellent test characteristics in detecting Gram-negative infection and, unlike urinary nitrites, may have some utility in detecting Gram-positive infections as well. Watch for further studies on this innovation.