Structure and Normal Values of the Leukocyte Differential
Leukocytes are a heterogeneous group of blood cells with protective functions, comprising five main types: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. In a healthy adult, the percentages of these elements in the blood fall within strict normal ranges:
- Segmented neutrophils: 51–67%
- Band neutrophils: 3–5%
- Immature neutrophils (metamyelocytes): 0–1%
- Lymphocytes: 21–35%
- Monocytes: 4–8%
- Eosinophils: 2–4%
- Basophils: 0.5–1%
- Myelocytes are normally absent.
Shifts in the Leukocyte Differential
To assess the severity of a condition and the nature of an inflammatory process, the concept of a leukocyte differential shift is used:
- A left shift is characterized by an increase in band neutrophils, as well as the appearance of immature forms and myelocytes. This is observed in acute infections, acidosis, physical exhaustion, and comatose states.
- A right shift is manifested by the appearance of hypersegmented neutrophils in the blood.
For an in-depth evaluation, the shift index (SI) is used, calculated as the ratio of the sum of myelocytes, metamyelocytes, and band neutrophils to segmented neutrophils. Normally, this value is 0.06.
Neutrophilia and Neutropenia
Quantitative changes in the neutrophil lineage play a key role in diagnosis:
- Neutrophilia is an elevation in cell levels. Causes include inflammatory processes, malignancies, the postoperative period, ischemic tissue necrosis (infarctions), endogenous intoxication (uremia), as well as certain medications and physical exertion.
- Neutropenia is a reduction in levels. An isolated form is associated with a deficiency of precursors in the bone marrow. Absolute granulocytopenia is observed in severe infections (sepsis, pertussis), hematological disorders, immune dysregulation, and following cytotoxic therapy.
Lymphocytosis and Lymphopenia
Changes in the lymphocytic lineage are divided into absolute and relative:
- Lymphocytosis (absolute > 3.5 × 10⁹/L, relative > 40%) frequently accompanies viral infections (ARVI, herpes, rubella), as well as blood disorders like lymphocytic leukemia.
- Lymphopenia (decreased lymphocyte count) can be relative during acute infections with enhanced granulocytopoiesis. Absolute lymphopenia is characteristic of immunodeficiency states (AIDS, DiGeorge syndrome), Hodgkin lymphoma, ionizing radiation exposure, and corticosteroid therapy.