Granulocytes in the blood

Types of granulocytes and their morphology

Granulocytes are produced in the bone marrow. During development, they follow a common evolutionary pathway up to the promyelocyte stage, after which their paths diverge. Mature forms are differentiated using immersion microscopy of smears (Romanowsky-Giemsa stain) based on the type of specific granularity:

• Neutrophils: the cytoplasm contains abundant, very fine, "dust-like" granularity that acquires a pinkish-purple hue.
• Eosinophils: easily recognized by their coarse granularity of a saturated scarlet color. These granules fill the entire cytoplasm, making the cell resemble a cluster of red caviar.
• Basophils: have coarse, structurally heterogeneous granularity of a very dark — purple or nearly black — color.

Normally, only mature elements circulate in the peripheral bloodstream — segmented cells (of all three types) and a small number of band neutrophils (less frequently, eosinophils). Mature forms are characterized by smaller sizes. Their nuclei are dark, dense, appearing as curved bands or divided into separate segments connected by thin filaments. Nucleoli are never present in such nuclei.

Young, immature forms (myeloblasts, promyelocytes, myelocytes, and metamyelocytes) are not found in the blood of a healthy person. Morphologically, these are large cells with a large, pale, round, or slightly indented nucleus. The chromatin pattern is delicate and fine, and nucleoli are often visualized within the nucleus.

Degenerative forms of leukocytes

In severe pneumonia, infections, and various purulent-inflammatory processes, degenerative changes may occur in granulocytes. Their detection serves as an important laboratory sign of severity.

1. Toxic granularity and cytoplasmic vacuolization. Under the influence of a strong infectious or toxic agent, coagulation of cytoplasmic proteins occurs. Large, coarse, basophilic-stained granules and pale areas — vacuoles — appear in neutrophils. Such a picture often accompanies severe pathologies with pronounced intoxication (e.g., severe lobar pneumococcal pneumonia).
2. Nuclear hypersegmentation. If a neutrophil nucleus consists of 6 or more segments, this reflects a nuclear shift to the right. This change occurs not only in severe infections but also in vitamin B₁₂- and folate-deficiency anemia, as well as in certain leukemias.

Special attention is paid to eosinopenia (a decrease in the eosinophil count). If it develops in patients with pneumonia combined with leukopenia, neutropenia, and a left shift of the differential, this is an extremely unfavorable prognostic sign. Such a combination indicates a sharp drop in the body's resistance.

Granulocytes in leukemias

Assessment of granulocyte maturity is a fundamental stage in the morphological diagnosis of leukemias. The main criterion is the examination of bone marrow aspirates (via sternal puncture or trephine biopsy). Smears are analyzed for the ratio of mature to immature forms.

• Acute leukemia. Characterized by the presence of a specific sign in the blood — the hiatus leukemicus phenomenon (leukemic gap). Blast cells (exceeding 10–20% in proportion) and fully mature granulocytes are present simultaneously in the smear. However, intermediate maturing forms are completely absent. In the bone marrow, normal hematopoietic lineages are displaced by blasts.
• Chronic leukemia (using CML as an example). Unlike the acute process, in chronic myeloid leukemia, tumor cells partially retain the ability to differentiate. A sufficient number of morphologically mature granulocytes, as well as all transitional stages of maturation, are found in the blood and bone marrow. The leukocyte count in the peripheral blood may exceed 300·10⁹/L.

Class and exam questions

What else to study on this topic

• Absolute and relative lymphocytosis in infections
• Morphology and diagnostic significance of the monocyte lineage
• Lymphocytopenia and T-cell immunity deficiency
• Morphological features of chronic lymphocytic leukemia (CLL)
• Botkin-Kleine-Gumprecht shadows: causes of appearance in the smear
• Immunophenotyping and cytochemical examination of the bone marrow

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.