Mechanisms of Leukopenia Development
The pathogenesis of a decreased leukocyte count is based on four main mechanisms:
- Excessive cell destruction. This occurs in the vascular bed or hematopoietic organs. The primary causes include ionizing radiation and antileukocyte antibodies. Medications (such as aminophenazone, sulfonamides, and barbiturates) acting as haptens play an important role. They stimulate antibody production, leading to leukocyte agglutination and death.
- Leukocyte redistribution. Under the influence of biologically active substances (chemotaxins, adhesion activators), cells temporarily accumulate in specific regions of the vascular bed. This causes a decrease in their count elsewhere, creating a picture of "false" (pseudo-) leukopenia in the peripheral blood.
- Increased loss by the body. This occurs during acute or chronic blood loss, as well as massive plasmarrhea and lymphorrhea. Typical examples include extensive burns and chronic purulent processes (peritonitis, endometritis, osteomyelitis).
- Hemodilution leukopenia. This is associated with blood dilution. It is observed in hypervolemia (transfusion of large volumes of plasma or plasma substitutes) or when fluid shifts from tissues into vessels along an osmotic/oncotic pressure gradient (in hyperaldosteronism, hyperglycemia, hyperalbuminemia).
Clinical and Morphological Manifestations of Leukopenia
A decrease in cell count can affect all differentiation pathways (general leukopenia) or predominantly one of them, causing isolated conditions: lymphocytopenia, monocytopenia, neutropenia, basopenia, or eosinopenia.
An important indicator is the dynamics of immature neutrophil forms (band cells, metamyelocytes):
- A decrease in their number in the early stages indicates suppression of the regenerative capacity of hematopoietic tissue.
- An increase in their number (a left shift) against the background of persistent leukopenia after eliminating the causative factor indicates the activation of leukopoiesis.
Leukopenia often reveals signs of cell degeneration and destruction (primarily in neutrophils and monocytes). Morphological changes include:
- Altered cell contours (poikilocytosis) and the presence of cells of varying sizes (anisocytosis).
- Shrinkage or swelling.
- Appearance of vacuoles, toxic granulation, and cytoplasmic inclusions.
- Nuclear hypersegmentation.
- Nuclear shrinkage (pyknosis) and breakdown (karyorrhexis).
Degenerative Nuclear Shifts
Changes in the leukocyte differential count during leukopenia are often accompanied by specific shifts:
- Degenerative left shift: a large number of degenerative leukocyte forms appear in the blood, the proportion of segmented neutrophils decreases, while there is a moderate increase in band neutrophils and metamyelocytes.
- Degenerative right shift: characterized by an increased number of segmented neutrophils with prominent signs of degeneration. There is no accompanying increase in band cells.
Features of Leukocytosis
An increase in the total leukocyte count or specific subsets (lymphocytosis, monocytosis, granulocytosis) directly depends on the nature of the causative factor. Based on their biological significance, leukocytoses are divided into two main groups: physiological and pathological.
Hemoconcentrational leukocytosis requires special attention:
- Cause: systemic hypohydration of various origins (recurrent vomiting, diarrhea, polyuria) leading to hypovolemia.
- Pathogenesis: the total (absolute) number of leukocytes in the body remains normal, but their concentration per unit volume of blood increases due to hemoconcentration and decreased plasma volume.
- Diagnostic sign: concurrent with leukocytosis, the blood shows an elevated count of other formed elements—erythrocytes and platelets.