Supplementary Material for: Neutrophil Gelatinase-Associated Lipocalin as a Diagnostic Marker for Acute Kidney Injury in Oliguric Critically Ill Patients: A Post-Hoc Analysis

<strong><em>Background:</em></strong> Oliguria occurs frequently in critically ill patients, challenging clinicians to distinguish functional adaptation from serum-creatinine-defined acute kidney injury (AKI<sub>sCr</sub>). We investigated neutrophil gelatinase-associated lipocalin (NGAL)'s ability to differentiate between these 2 conditions. <b><i>Methods:</i></b> This is a post-hoc analysis of a prospective cohort of adult critically ill patients. Patients without oliguria within the first 6 h of admission were excluded. Plasma and urinary NGAL were measured at 4 h after admission. AKI<sub>sCr</sub> was defined using the AKI network criteria with pre-admission serum creatinine or lowest serum creatinine value during the admission as the baseline value. Hazard ratios for AKI<sub>sCr</sub> occurrence within 72 h were calculated using Cox regression and adjusted for risk factors such as sepsis, pre-admission serum creatinine, and urinary output. Positive predictive values (PPV) and negative predictive values (NPV) were calculated for the optimal cutoffs for NGAL. <b><i>Results:</i></b> Oliguria occurred in 176 patients, and 61 (35%) patients developed AKI<sub>sCr</sub>. NGAL was a predictor for AKI<sub>sCr</sub> in univariate and multivariate analysis. When NGAL was added to a multivariate model including sepsis, pre-admission serum creatinine and lowest hourly urine output, it outperformed the latter model (plasma p = 0.001; urinary p = 0.048). Cutoff values for AKI<sub>sCr</sub> were 280 ng/ml for plasma (PPV 80%; NPV 79%), and 250 ng/ml for urinary NGAL (PPV 58%; NPV 78%). <b><i>Conclusions:</i></b> NGAL can be used to distinguish oliguria due to the functional adaptation from AKI<sub>sCr</sub>, directing resources to patients more likely to develop AKI<sub>sCr</sub>.