Urinary Neutrophil Gelatinase-Associated Lipocalin and Serum Cystatin C as Early Biomarkers of Acute Kidney Injury in Critically Ill Children: Single-Center PICU Cohort, 2024–2025

Introduction: We have explored the use of early biomarkers for the timely identification of acute kidney injury (AKI) in critically ill children. Design: Single-center cohort study. Setting: Tertiary medical-surgical PICU in Coimbra, Portugal. Patients: Pediatric patients admitted for longer than 48 hours over a 10-month period during 2024–2025. Interventions: None. Measurements and Results: Among 75 patients (55.3% male; median age 3.9 yr), 22 patients (29.3%) developed AKI (defined by Kidney Disease Improving Global Outcomes criteria) on day 1. On comparing those with or without AKI, urinary neutrophil gelatinase-associated lipocalin (uNGAL) levels were elevated on day 1 ( p < 0.001), day 2 ( p = 0.003), and day 3 ( p = 0.013) in AKI patients. Cystatin-C (Cys-C) was only increased on day 1 ( p = 0.013). Shock ( p < 0.001) and vasoactive drug use ( p = 0.007) were more commonly present in AKI patients, who also had lower albumin ( p = 0.012), platelets ( p = 0.001), and bicarbonate level ( p = 0.032). AKI patients also had higher C-reactive protein (CRP; p = 0.018), procalcitonin ( p = 0.002), and lactate concentration ( p = 0.022). Shock and CRP were associated with greater odds (presented as odds ratio [OR] with 95% CI) of AKI, respectively as: OR, 6.10 (95% CI, 1.50–16.52); p = 0.002; and OR, 1.07 (95% CI, 1.00–1.12); p = 0.022; as well as day 1 Renal Angina Index (RAI; OR, 1.10 [95% CI, 1.03–1.17]; p = 0.005). On day 1, the discrimination performance (using the area under the receiver operating characteristic curve [AUC]) for AKI was good-to-excellent for, respectively: uNGAL, 0.847 (95% CI, 0.74–0.96); p value of less than 0.001; and blood urea nitrogen, 0.848 (95% CI, 0.75–0.95); p value of less than 0.001. Regarding uNGAL, the pretest probability of AKI was 29.3%, and the posttest probability of AKI on finding a uNGAL greater than 87 ng/mL rose to 73.1%, which leaves significant diagnostic uncertainty. Also, the day 1 RAI was an acceptable to good discriminator of the severity of AKI in those identified with AKI: AUC, 0.796 (95% CI, 0.60–0.99); p = 0.019. Conclusions: In our PICU cohort, day 1 uNGAL level greater than 87 ng/mL has good-to-excellent discriminative capacity in identifying AKI, but the diagnostic uncertainty of AKI remains.