BACKGROUND: Diabetic ketoacidosis (DKA) is well-known to be associated with increased levels of inflammatory markers including cytokines. Interestingly, an elevated white blood count (WBC) has been associated with a higher prevalence of acute and chronic diabetes metabolic complications, including DKA, and micro- and macrovascular complications (Tong et al., 2004; Xu et al., 2013). However, very few studies have looked at the relationship between WBC differential and the severity of DKA. For instance, a study looking at platelet-to-lymphocyte ratio found it to be a significant predictor of mortality in DKA patients admitted to the intensive care unit (Liu et al., 2016). Aim: The goal of the present study is to investigate the relationship between the WBC differential and the severity of DKA. Method: This study was conducted at Dalhousie University-affiliated hospitals in Nova Scotia, Canada. Ethics approval was obtained. The medical records of 646 emergency visits for 338 patients between November 2015 to December 2018 with a provisional diagnosis of DKA were retrospectively reviewed. 84 records were excluded due to non-anion gap metabolic acidosis, and 66 were excluded due to radiological or microbiological evidence of infection (positive urine, stool or blood cultures, pneumonia, etc.). Only the first set of blood investigations were analyzed to avoid post-treatment changes in blood composition. WBC differential (neutrophils, basophils, eosinophils, immature granulocyte, lymphocytes, metamyelocytes, monocytes, and myelocytes) and severity of DKA based on pH value (mild: 7.25–7.30, moderate: 7.24-7.00, and severe: <7.00) were analyzed. Result: A total of 496 visits for 277 patients were analyzed, with about 1:1.2 male-to-female ratio and median age of 36.5 years (range 18–90 years), with no significant differences in sex or age in relation to the severity of DKA (P-value= 0.68 and 0.16, respectively). Leukocytosis (WBC >11 x10(9)/L) was seen in 65% (n=314). 32% (n=158) had mild DKA, while 56% (n=273) and 1% (n=57) had moderate and severe DKA, respectively. With increased severity of DKA, higher WBC count and hemoglobin levels were observed (P-value= 0.002 and 0.037, respectively). This is not unexpected due to hemoconcentration. However, monocytes, immature granulocytes, and basophils (percentage unit of the total WBC) increased with the severity of DKA (P-value: 0.004, <0.001, and <0.001, respectively). On the other hand, lymphocytes displayed an inverse relationship to DKA severity (P-value: 0.015). In contrast, eosinophils & neutrophils had no significant correlation to the DKA severity (P-value= 0.96, and 0.44, respectively). Conclusion: The WBC differential (namely, monocytes, immature granulocytes, basophils, & lymphocytes) is associated with the severity of DKA. We propose that the WBC differential be further studied as a prognostic indicator in patients with DKA.