Hyperleukocytosis in Pediatric Patients with Acute Lymphoblastic Leukemia: Demographic and Clinical Characteristics

<b>Background</b>: Hyperleukocytosis, defined as a total leukocyte count of more than 50,000/mm³ leukocytes, occurs in almost one in five children with acute lymphoblastic leukemia (ALL). It represents an unfavorable prognostic factor in this disease. The aim of the following study was to describe demographic and clinical features in patients with hyperleukocytosis and their relationship with leukocyte count. <b>Methods</b>: We retrospectively analyzed the available medical data of patients with ALL diagnosed and treated at the University Children's Hospital in Lublin between 2017 and 2024. <b>Results</b>: Of the 97 patients, 10 (10.3%) had hyperleukocytosis. They were significantly more likely to be older boys diagnosed with T-ALL. The group with hyperleukocytosis had a higher mortality rate. The presence of hyperleukocytosis also correlated with the presence of petechiae, thrombocyte and neutrophil counts, and LDH activity. Patients with hyperleukocytosis also experienced a higher incidence of infections as a complication of therapy as leukocyte counts increased. <b>Conclusions</b>: Hyperleukocytosis, although rare, is an important factor in the course of ALL, both clinically and prognostically.