Leukocytosis

Mechanisms of development

Pathophysiology distinguishes four key mechanisms leading to an increase in the number of leukocytes in the bloodstream:

1. Enhanced normal leukopoiesis. Active proliferation of bone marrow cells occurs, accompanied by their normal differentiation into mature forms. This is so-called true leukocytosis.
2. Leukocyte redistribution. Cells change their localization within the vascular bed without altering their total number in the body.
3. Neoplastic production. Uncontrolled formation of atypical leukocytes characteristic of hemoblastoses.
4. Hemoconcentration. Relative increase in cell count due to blood thickening.

Redistributive (false) leukocytosis

This type of leukocytosis is exclusively temporary. Under the action of biologically active substances (chemotaxins, adhesion stimulators), leukocytes massively accumulate in certain regions, while in others their count drops. The peripheral blood picture thus becomes "false".

Main causes:

• Shock states (anaphylactic, transfusion, traumatic shock). Leukocytes settle in the microvessels of the lungs, liver, and intestinal walls.
• Significant physical exertion (myogenic leukocytosis).

Characteristic features:

• Signs of hematopoietic tissue hyperplasia are absent.
• Only mature cell forms accumulate in the blood.
• There is no shift of the leukocyte formula to the left.

Physiological and neoplastic leukocytoses

Physiological leukocytoses are always adaptive in nature. They are quantitatively and qualitatively adequate to the factor that caused them and increase the body's resistance by activating leukocyte functions (e.g., phagocytosis). They are divided into two groups:

• Functional: associated with physiological activity (pregnancy, digestion, muscular work).
• Protective-adaptive: occur in response to inflammation, stress, or tissue necrosis (after infarctions, strokes, trauma).

Neoplastic leukocytoses develop in leukemias. Unlike physiological ones, they have no adaptive significance. Pathological cells exhibit signs of tumor atypia and are functionally defective: their phagocytic activity and ability to release cytokines are sharply reduced.

Nuclear shift of neutrophils

Nuclear shift is a change in the ratio between mature and immature neutrophils. The criterion for evaluation is the appearance of the nucleus (its shape, size, staining) upon smear microscopy.

• Shift to the left means the appearance of immature forms in the blood. Hyporegenerative, regenerative, hyperregenerative, and regenerative-degenerative shifts are distinguished. For example, in a hyperregenerative shift, the leukocyte count reaches $20–25 \times 10^9/\text{L}$, and numerous band cells, metamyelocytes (juvenile), and myelocytes appear in the blood.
• Shift to the right (degenerative) is characterized by the predominance of mature segmented forms.

Terminology and evaluation rules

To describe an increase in the number of specific cells, the endings -philia or -osis are used (neutrophilia, lymphocytosis, monocytosis). To denote a decrease, the ending -penia is used (eosinopenia, lymphopenia). A special condition is agranulocytosis, characterized by a sharp decrease or complete absence of all granulocytes (neutrophils, eosinophils, basophils).

> Golden rule: When analyzing blood, always evaluate not only the relative (percentage), but also the absolute cell content.

Relative values show 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. The direction of changes in percentages and absolute numbers does not always coincide.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Detailed characteristics of types of shifts to the left (hypo-, regenerative, regenerative-degenerative)
• Mechanisms of development of absolute and relative thrombocytosis
• Pathogenesis of thrombocytopenias in bone marrow hypoplasia and hyperplasia
• Metabolic disorders in megakaryocytes (decrease in glycogen and enzyme activity)
• Peripheral blood changes in hemorrhagic syndrome (platelet anisocytosis, posthemorrhagic anemia)

Other topics in "Chapter 21. Typical Pathology Forms of the Blood System"

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