A-309 Multicenter Performance Evaluation of the ProNephro AKITM Assay and Sample Stability in Pediatric Patients
Authors: Malaeb H , Zilka S , Jarden A , Klause U , El-Khoury J , Tsaniklides N , Colón-Franco J M 
Published: October 2024

Abstract

Background
Acute Kidney Injury (AKI), defined by increased serum creatinine or decreased urine volume, is highly prevalent in critically ill pediatric patients. Those who develop AKI experience worsened outcomes, raising the need for accurate and early biomarkers for AKI. Relying in serum creatinine for AKI diagnosis is unreliable due to its diagnostic inaccuracy and delayed rise in the AKI pathophysiology. Neutrophil Gelatinase-Associated Lipocalin (NGAL) is a novel and widely studied biomarker for early identification of AKI. During pathological progression, NGAL is elevated in blood and urine within two hours of the insult, making it useful for early diagnosis and management of kidney injury in critically ill children. This study aims at evaluating the performance characteristics of a quantitative test for NGAL in urine intended for use in critically ill pediatric patients, and investigating the stability of NGAL in pediatric urine.

Methods
The ProNephroAKITM is a particle-enhanced turbidimetric immunoassay on the Roche cobas® c501 analyzer to measure NGAL quantitatively in urine in pediatric patients 3 months to 21 years of age. These studies were approved by the respective institutional review boards. The limits of blank (LOB), detection (LOQ) and quantitation (LOQ) were determined following CLSI EP17A2. Linearity was assessed across the measurement range (MR) of 50-3000 ng/mL. The assay repeatability, between-run, between-day and total imprecision were determined in pediatric urine samples (n=9, covering the MR) and controls (n=2) following CLSI EP5-03 guidelines. Likewise, multisite reproducibility was evaluated in pediatric urine (n=7, covering the MR) and controls (n=2) in 3 laboratories and alternating operators. The assay specificity was assessed in the presence of several endogenous and exogeneous substances (e.g. drugs, contrast agents), potential related cross-reactant molecules, and several pH-values. The stability of NGAL in urine was evaluated using freshly collected pediatric urine samples covering the MR from 16 consented patients after storage at ambient (15-30°C), refrigerated (2-8°C), and frozen temperatures (≤-70°C), and following 3 freeze/thaw cycles.

Results
The ProNephroAKITM is linear across the MR of 50-3000 ng/mL. The LOB, LOD and LOQ were 9, 14 and 18 ng/mL, respectively. The coefficients of variation (CVs) for repeatability, between-run, between-day and total precision were ≤5.0%, ≤3.1%, ≤1.7% and ≤4.9%, respectively in urine and control samples. The reproducibility across 3 independent laboratories was ≤6.6%. The recovery of NGAL was not significantly affected by endogenous substances, contrast agents, pH (3.3-10.3), and common and special pharmaceutical compounds (exception: very high Cefepime concentrations may decrease NGAL), and potential cross-reactants. Freshly collected urine samples spanning concentrations from 71-2,373 ng/mL were stable (±10% recovery) for 2 days at ambient, 4 days refrigerated and 13 months frozen, and after 3 freeze/thaw cycles.

Conclusions
We report the performance characteristics of the ProNephroAKITM assay, including excellent precision and adequate reproducibility across 3 laboratories, sensitivity, specificity, and urine sample stability. The test was determined to meet the analytical performance required for clinical use in critically ill pediatric patients at risk of developing or having persistent AKI.