U-shape relationship of white blood cells with acute kidney injury and mortality in critically Ill patients

Low or high counts of white blood cells (WBCs) and WBC subtypes can be a predictor of morbidity and mortality in several clinical settings. However, the correlations of WBC and its subtypes with acute kidney injury (AKI) and mortality remain unresolved in critically ill patients. The counts of WBC and subtypes, such as neutrophil, lymphocyte, monocyte, and eosinophil, were measured in 2,079 patients admitted to the intensive care unit (ICU) from June 2004 through June 2010. The non-linear relationship between WBC counts and AKI risk was initially explored by a restricted cubic spline analysis. The odds ratios (ORs) for AKI and 1-year mortality were calculated after adjustment for multiple covariates. The relationship between WBC counts and AKI risk was U-shaped. Accordingly, we divided patients into quintiles according to the counts of WBC or subtypes. The 1^st and 5^th quintiles of WBC counts had greater ORs for AKI (1.42 and 2.05, respectively) and mortality (1.40 and 1.36, respectively) compared with the 3^rd quintile. After stratification by WBC subtype, the 5^th quintile of neutrophil counts and the 1^st quintiles of lymphocyte and monocyte counts tended to have higher ORs for AKI (1.69, 1.40, and 1.77, respectively). For mortality, the 1^st quintiles of neutrophil, lymphocyte, and eosinophil counts were associated with higher mortality compared with the 3^rd quintile (the ORs were 1.48, 1.57, and 1.42, respectively). Both leukopenia and leukocytosis are associated with AKI and mortality risk in critically ill patients. This result may be attributable to the change in the subtype counts.