Leukocytos

Leukocytosis, also called leukocytos, is the rise in the number of white blood cells (leukocytes) in the peripheral blood. In adults, a total leukocyte count above about 11,000 cells per microliter is commonly used as a threshold for leukocytosis, though reference ranges vary by laboratory and age.

Most leukocytosis is reactive or physiologic, arising from infections, inflammatory or tissue injury, stress, strenuous exercise, pregnancy, or smoking. Medications such as corticosteroids or granulocyte colony-stimulating factors can increase counts. Less commonly, leukocytosis results from hematologic malignancies such as chronic myeloid leukemia or other myeloproliferative disorders.

Leukocytosis is not a single disease but a sign. It is classified by the predominant leukocyte type: neutrophilic leukocytosis (most common, seen with bacterial infection, inflammation, or stress); lymphocytosis (viral infections, certain pertussis, chronic infections); monocytosis; eosinophilia; basophilia. A left shift, with increased immature neutrophils such as band cells, suggests an active bone marrow response to infection or inflammation.

Evaluation includes complete blood count with differential, peripheral smear, and targeted tests (cultures, imaging, serology) to identify the cause. Very high counts (leukocytosis >50,000–100,000) raise concern for leukostasis in leukemia or myeloproliferative neoplasms. Differentiating reactive leukocytosis from leukemia relies on morphology, rate of rise, patient findings, and sometimes bone marrow examination.

Management targets the underlying cause. Mild, asymptomatic leukocytosis may require no specific therapy beyond observation, while significant infection or malignancy requires appropriate treatment. Prognosis depends on the underlying condition rather than the leukocytosis alone.