Reference values for urinary neutrophil gelatinase-associated lipocalin (NGAL) in pediatric age measured with a fully automated chemiluminescent platform.

BACKGROUND: Neutrophil gelatinase-associated lipocalin (NGAL) has been suggested as the most promising biomarker of acute kidney injury. However, there are no reliable data on analytical sensitivity and reference limits of urinary NGAL (uNGAL) assay in pediatric age. The aim of the present study is to evaluate the analytical sensitivity and the reference range of uNGAL measured in urine specimens of pediatric age with the fully automated platform ARCHITECT i1000. METHODS: A total of 333 urine samples were collected from 25 healthy newborns (16 males and 9 females; age 1-4 days) and 308 children (150 males and 147 females; mean age 80.7 months, range 0.63-248 months) and assayed for uNGAL by two different Italian centers (Department of Laboratory Medicine of the Fondazione Toscana G. Monasterio of Pisa and Massa and the Clinical Pathology Laboratory Unit of Istituto Giannina Gaslini of Genova). RESULTS: The calculated limits of blank (LOB) and detection (LOD) values were 0.5 ng/mL and 0.95 ng/mL, respectively. The distribution of uNGAL values approximated a log-normal distribution (median 5.2 ng/mL, interquartile range 2.5-12.8 ng/mL, 99th percentile 117.6 ng/mL). uNGAL values of the 25 neonates were significantly higher than those of 308 children (neonates: mean 44.2 ng/mL, median 30.3 ng/mL, range 5.2-137.4 ng/mL; children: mean 10.2 ng/mL, median 4.6 ng/mL, range 0.2-146.7 ng/mL; p<0.0001). CONCLUSIONS: uNGAL assay shows a good analytical sensitivity and imprecision, which allows the measurement of uNGAL values around the cut-off value (i.e., 117.6 ng/mL) with an imprecision <5 CV%. The distribution of uNGAL values in pediatric age approximates a log-normal distribution, with values which are higher in neonates compared to children.

Identification and structural characterization by LC-ESI-IONTRAP and LC-ESI-TOF of some metabolic conjugation products of homovanillic acid in urine of neuroblastoma patients.

The levels of urinary catecholamine metabolites, such as homovanillic acid (HVA) and vanillylmandelic acid, are routinely used as a clinical tool in the diagnosis and follow-up of neuroblastoma (NB) patients. Recently, in the Clinical Pathology Laboratory Unit of G. Gaslini Children Hospital, a commercial method that employs liquid chromatography coupled to electrochemical detection (LC-EC) has been introduced for the measurement of these metabolites in the routine laboratory practice. Using this LC-EC method, an unknown peak could be observed only in samples derived from NB patients. To investigate the nature of this peak, we used a combination of liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) and liquid chromatography-ion trap tandem mass spectrometry (LC-IT-MS). The first approach was used to obtain the elemental composition of the ions present in this new signal. To get additional structural information useful for the elucidation of unknown compounds, the ion trap analyzer was exploited. We were able to identify not just one, but three unknown signals in urine samples from NB patients which corresponded to three conjugated products of HVA: HVA sulfate and two glucuronoconjugate isomers. The enzymatic hydrolysis with ß-glucuronidase confirmed the proposed structures, while the selective alkaline hydrolysis allowed us to distinguish the difference between phenol- and acyl-glucuronide of HVA. The latter was the unknown peak observed in LC-EC separations of urine samples from NB patients.