Leukemoid reaction: A 21st-century cohort study.

Area of Science:

• Hematology
• Oncology
• Infectious Diseases

Background:

• Leukemoid reaction, defined by a leukocyte count >50 × 10⁹/L, is a rare but significant clinical finding.
• Limited data exists on the clinical relevance and prognosis of leukemoid reactions.
• This study investigates the etiology and outcomes of patients with leukemoid reactions.

Purpose of the Study:

• To analyze the causes and outcomes of leukemoid reactions.
• To identify factors associated with mortality in patients with leukemoid reactions.
• To provide insights into the clinical management of this condition.

Main Methods:

• Retrospective cohort study of patients with leukocyte count >50 × 10⁹/L.
• Inclusion criteria: patients >18 years old at a Brazilian tertiary hospital (Jan 2016 - July 2018).
• Analysis included demographics, blood counts, clinical features, etiology diagnostics, survival analysis (Kaplan-Meier), and logistic regression for mortality predictors.

Main Results:

• 267 cases identified; 60% (162) secondary to hematopoietic neoplasm, 40% (105) true leukemoid reaction.
• True leukemoid reaction causes: infection (59), nonhematopoietic neoplasm (17), other (29).
• Significant difference in mortality (P < .001); lower hemoglobin, older age, and increased segmented neutrophils associated with higher risk.

Conclusions:

• Infection is the most common cause of true leukemoid reaction, involving various microorganisms.
• Paraneoplastic leukemoid reaction is also a frequent cause.
• Both conditions are associated with high mortality, posing a major medical challenge.