Urine Output Thresholds for Defining and Staging Pediatric AKI

Although pediatric acute kidney injury (AKI) is associated with considerable morbidity and mortality, a precise definition, particularly regarding urine output (UO) thresholds, remains elusive. Adriana Torres de Melo Bezerra Girão and colleagues wanted to understand the optimal thresholds for defining and staging AKI in neonates and children aged 1 to 24 months and compare them with currently used Kidney Disease: Improving Global Outcomes (KDIGO) criteria.  

They conducted a prospective cohort study from 2018 to 2023 of patients who had cardiac surgery at a reference center in Brazil, had indwelling urinary catheters up to 48 hours after surgery, and had at least two serum creatinine measurements, including one before surgery. The primary study outcome was a composite of severe AKI (stage 3 AKI diagnosed solely by serum creatinine criterion), kidney replacement therapy, or hospital mortality. 

Of the 1,024 patients included in the study, 772 were younger children (aged 1 to 24 months) and 253 were neonates. The lowest UO at 24 hours as a continuous variable demonstrated good discriminatory capacity for the composite outcome in both groups (area under the curve–receiver operating characteristic [AUC-ROC], 0.75; 95% CI, 0.70-0.81 for neonates and AUC-ROC, 0.74; 95% CI, 0.68-0.79 for younger children). In the neonate group, the optimal thresholds were 3.0, 2.0, and 1.0 mL/kg per hour. In the group of younger children, the best thresholds were 1.8, 1.0, and 0.5 mL/kg per hour.  

Those optimal thresholds were then used for modified AKI staging for each age group. In the group of younger children, the modified criteria had discriminatory capacity comparable to that of the adult KDIGO criteria; the net improvement with the reclassification was near zero.  

However, in the neonate group, the modified criterion was associated with discriminatory capacity superior to that of the current KDIGO criteria (AUC-ROC, 0.74; 95% CI, 0.67-0.80 vs AUC-ROC, 0.68; 95% CI, 0.61-0.75; P<.05). The modified criterion was also associated with a net improvement compared with the neonatal KDIGO criteria (AUC-ROC, 0.74; 95% CI, 0.67-0.80 vs AUC-ROC, 0.68; 95% CI, 0.61-0.75; P<.05).  

In summary, the study results suggest that KDIGO criteria for the definition and staging of AKI in neonates may need adjustment. 

Source: Clinical Journal of the American Society of Nephrology