Подсчет лейкоцитарной формулы (микроскопия мазка крови) (венозная кровь)

The leukocyte differential (WBC differential, leukogram) reports the relative distribution of neutrophils, lymphocytes, monocytes, eosinophils, and basophils in peripheral blood. By characterizing these white blood cell populations, the test helps assess the integrity of host defense and the pattern of inflammatory response. Clinically, the leukocyte differential is used to evaluate infectious processes and to gauge the immune response in viral illnesses; to support assessment of allergic disease and suspected parasitic infection; and to identify unfavorable hematologic effects of medications. It contributes to the differential diagnosis of leukemias and is used to track treatment response, including surveillance during and after chemotherapy.

Leukocytes arise from bone marrow stem cells, have short life spans, and undergo continuous renewal. Production increases with tissue injury as part of the normal inflammatory response. Five main leukocyte types—neutrophils, lymphocytes, monocytes, eosinophils, and basophils—perform distinct but coordinated roles mediated through cytokine signaling. Modern hematology analyzers perform automated differentials on thousands of cells, whereas manual review typically examines 100–200 cells. When the analyzer flags atypical forms or marked deviations from reference intervals, the differential is supplemented with microscopic examination of a blood smear. Smear review can reveal features consistent with infectious mononucleosis, help grade the severity of infectious processes, and characterize abnormal or blast populations in leukemia. Neutrophils are the most abundant and are first to respond at sites of tissue damage, where they phagocytose bacteria. Mature neutrophils have segmented nuclei (also termed segmented neutrophils or polymorphonuclear leukocytes), while immature forms (bands) have nonsegmented nuclei. Lymphocytes, comprising T and B cells (not individually enumerated in the differential), are central to antiviral defense and control of chronic infection. B cells produce antibodies that opsonize antigen-bearing targets, facilitating clearance by neutrophils and monocytes, whereas T cells destroy infected cells and can recognize and eliminate malignant cells. Monocytes circulate for approximately 20–40 hours before entering tissues and differentiating into macrophages, which both phagocytose and present antigens to lymphocytes and help sustain inflammation in chronic disorders such as rheumatoid arthritis. Eosinophils, present in smaller numbers, can phagocytose but are best known for antiparasitic activity and participation in allergic reactions. Basophils are few in number, migrate into tissues to become mast cells, and, upon activation, release histamine that contributes to pruritus, burning, and erythema in allergic responses.