Mechanisms of Development
Pathophysiology identifies four key mechanisms leading to an elevated white blood cell count in the circulation:
- Enhancement of normal leukopoiesis. Active bone marrow cell proliferation occurs alongside normal differentiation into mature forms. This is known as true leukocytosis.
- Leukocyte redistribution. Cells change their localization within the vascular bed without altering their total body count.
- Neoplastic production. Uncontrolled generation of atypical leukocytes, characteristic of hematologic malignancies.
- Hemoconcentration. A relative increase in cell concentration due to decreased plasma volume (blood thickening).
Redistribution (False) Leukocytosis
This type of leukocytosis is strictly transient. Under the influence of bioactive substances (chemotaxins, adhesion molecules), leukocytes accumulate massively in certain vascular beds while dropping in others. The peripheral blood picture thus becomes "false" (redistributive).
Main Causes:
- Shock states (anaphylactic, transfusion, or traumatic shock). Leukocytes marginate and sequester in the microvasculature of the lungs, liver, and intestinal walls.
- Strenuous physical exertion (myogenic leukocytosis).
Key Characteristics:
- Absence of hematopoietic tissue hyperplasia.
- Only mature cell forms accumulate in the blood.
- No left shift in the differential count.
Physiological and Neoplastic Leukocytosis
Physiological leukocytosis is always adaptive. It is quantitatively and qualitatively appropriate to the triggering stimulus and enhances bodily resistance by activating leukocyte functions (e.g., phagocytosis). It is divided into two groups:
- Functional: associated with normal physiological activity (pregnancy, digestion, muscular work).
- Protective-adaptive: occurs in response to inflammation, stress, or tissue necrosis (following myocardial infarction, stroke, or trauma).
Neoplastic leukocytosis develops in leukemias. Unlike physiological leukocytosis, it has no adaptive value. Pathological cells display features of neoplastic atypia and are functionally impaired: their phagocytic activity and cytokine-releasing capacity are drastically reduced.
Neutrophil Nuclear Shift
Nuclear shift refers to a change in the ratio between mature and immature neutrophils. The evaluation criterion is the morphology of the nucleus (its shape, size, and staining characteristics) assessed via blood smear microscopy.
- Left shift indicates the appearance of immature forms in the blood. Subtypes include hyporegenerative, regenerative, hyperregenerative, and regenerative-degenerative shifts. For example, in a hyperregenerative shift, the leukocyte count reaches $20–25 \times 10^9/\text{L}$, and numerous band cells, metamyelocytes (juvenile cells), and myelocytes appear in the blood.
- Right shift (degenerative) is characterized by the predominance of mature segmented-nuclear forms.
Terminology and Evaluation Rules
An increase in specific cell types is designated by the suffixes -philia or -cytosis (neutrophilia, lymphocytosis, monocytosis). A decrease is designated by the suffix -penia (eosinopenia, lymphopenia). A critical condition is agranulocytosis, characterized by a severe reduction or complete absence of all granulocytes (neutrophils, eosinophils, basophils).
> Golden Rule: When analyzing a complete blood count, always evaluate both the relative (percentage) and absolute cell counts.
Relative values indicate only the proportion of cells per unit volume. The true picture is reflected only by absolute values, which are calculated based on the total leukocyte count and the percentage of a specific cell type. Percentage changes and absolute count changes do not always correlate.