Introduction: Leukemoid reaction (leukocyte count >50 cells ×109 L) is a rare but extremely relevant finding. Since little has been published on this condition's clinical relevance and prognosis, we investigated leukemoid reaction in patients with a white blood cell count of >50 × 109 L, including etiology and outcomes.
Methods: This retrospective cohort study included all patients at a Brazilian tertiary hospital between January 2016 and July 2018 > 18 years with a total leukocyte count >50 cells×109 L. Demographics, complete blood count, clinical features, and the exams used to diagnose and determine leukemoid reaction etiology were analyzed. A Kaplan-Meyer survival analysis was performed, and a binary logistic regression model identified variables associated with death.
Results: Of the 267 cases with white blood cell count of >50 × 109 , 162/267 (60%) were secondary to hematopoietic neoplasm and 105/267 (40%) presenting as a true leukemoid reaction. The primary causes of the true leukemoid reaction cases were infection (59), nonhematopoietic neoplasm (17), or other causes (29). Patient deaths (66) differed significantly between groups (P < .001, log-rank [Mantel-Cox] Test). Lower hemoglobin, older age, and increased segmented neutrophil count were associated with increased risk of death.
Conclusions: This was a modern cohort analysis of leukemoid reactions, inclusive of all etiologies. The most common cause was infection, which involved several microorganisms. Paraneoplastic leukemoid reaction was also common. Both conditions have a poor prognosis with high mortality, being a major medical challenge.
Keywords: extreme neutrophilic leukocytosis; infection leukocytosis; leukemoid reaction; leukocytosis; paraneoplastic leukemoid reaction.
© 2019 John Wiley & Sons Ltd.