To explore the relationship between the neutrophil-to-lymphocyte ratio (NLR) and the 90-day mortality risk in severe patients with acute kidney injury (AKI), so as to evaluate the predictive value of NLR for the prognosis.

Retrospective analysis was made in 802 AKI patients who were admitted to the intensive care unit of the First Affiliated Hospital of Xi′an Jiaotong University from January 2015 to December 2019, and divided into low-NLR group (NLR<9) and high-NLR group (NLR≥9) according to the NLR level at admission. Differences were compared between the two groups in the underlying diseases, initial sequential organ failure assessment (SOFA), white blood cells (WBC), neutrophil percentage (NEU%), hemoglobin (Hb), platelet (PLT), lactic acid (Lac), pH, blood glucose (Glu), creatine kinase (CK), 90-day all-cause-death, and other variables. Logistic regression model was used to analyze the risk factors for 90-day mortality in critically ill patients with AKI. The receiver operating characteristic (ROC) curve was drawn, and the area under the ROC curve (AUC) was calculated to evaluate the predictive value of NLR for the 90-day mortality in critically ill patients with AKI.

There was no statistically significant difference in age, gender, ill AKI staging, and Glu between the two groups. In the high-NLR group, the levels of SOFA score, WBC, Neu%, Hb, PLT, BUN, SCr, Lac, and CK were higher, while BMI and pH were lower than those in the low-NLR group. The 90-day mortality rate was significantly higher in the high-NLR group than in the low-NLR group (32.6% vs 16%, P< 0.001). Multivariate logistic regression analysis showed that even after adjustment for age, gender, BMI, underlying disease factors, Lac value, AKI staging, and SOFA score, the NLR was still an independent predictor of 90-day mortality in critically ill patients with AKI (OR=2.402, 95%CI: 1.633-3.533, P<0.001). The AUC of the 90-day mortality risk prediction model based on traditional indicators (age, gender, BMI, underlying diseases, AKI staging, SOFA score, and Lac) was 0.761 (95%CI: 0.730-0.790), while the AUC of the 90-day mortality risk prediction model based on both traditional indicators and NLR was 0.783 (95%CI: 0.753 to 0.811), and the difference between the two models was statistically significant (P=0.0067).

NLR had a certain predictive value for the 90-day mortality risk in critically ill AKI patients, and might help improve the predictive ability of the model based on the traditional indicators.