Background: Leukocytosis is defined as a peripheral blood white blood cell (WBC) count >11,000/µL in adults. Because it has diverse causes and may have important diagnostic and management implications, this study investigated the etiologies of leukocytosis among hospitalized patients at Shohada-ye Ashayer Hospital in Khorramabad, Iran, from 2020 to 2023.
Methods: This retrospective, cross-sectional, descriptive study included hospitalized adults aged ≥18 years with a WBC count ≥11,000/µL. Patients were evaluated for age, sex, medical and medication history, fever, neutrophil percentage, and predominant clinical symptoms at admission. The primary cause of leukocytosis was determined based on the clinical diagnosis and treatment documented in the medical records.
Results: Among 317 patients, 194 had neutrophilic and 123 had lymphocytic leukocytosis. The causes of neutrophilic leukocytosis were leukemia in 71 patients (22.4%), acute infection in 63 (19.9%), collagen-vascular diseases in 31 (9.8%), corticosteroid use in 21 (6.6%), and leukemoid reaction in 8 (2.5%). The causes of lymphocytic leukocytosis were leukemia in 76 patients (24.0%), viral infections in 25 (7.9%), drug reactions in 13 (4.1%), and autoimmune diseases in 9 (2.8%). WBC counts exceeded 40,000/µL in 63 patients with leukemia and 3 with leukemoid reaction among those with neutrophilic leukocytosis, and in 72 patients with leukemia and 1 with viral infection among those with lymphocytic leukocytosis.
Conclusion: In this hospitalized population, WBC counts >40,000/µL were frequently associated with leukemia and, less commonly, leukemoid reactions or infection. At lower WBC counts, infectious, inflammatory, drug-related, and other underlying conditions should also be considered.
Implications for Patient Care: Markedly elevated WBC counts, particularly with neutrophilia or lymphocytosis, should prompt evaluation for hematologic malignancy and leukemoid reaction, while lower levels require broader assessment based on the clinical presentation, medical history, medications, and potential infectious or inflammatory conditions.