What Is Granulocytes: Definition, Types & Function

• by the presence of granulations in the cytoplasm;
• by a nucleus that generally has multiple lobes;

For this last characteristic, granulocytes are sometimes awarded the adjective polymorphonuclear or nucleopolymorphic.

In relation to the affinity of the granulations with the different types of dye, three varieties can be distinguished:

• Eosinophilic granulocyte;
• Basophilic granulocyte;
• Neutrophilic granulocyte.

What are

Granulocytes are white blood cells characterized by the presence of large granules in the cytoplasm, visible under an optical microscope after treatment with special dyes.

Based on the type of granulation and the response to the different types of dye, the following are distinguished:

• Neutrophils (which have affinity for neutral dyes);
• Eosinophils (which stain with acidic ones);
• Basophils (similar to basic dyes).

The presence of lobed nuclei also determines the definition of polymorphonuclear (due to the variously segmented appearance of the nucleus) or nucleopolymorphic.

Functions of granulocytes

Monocytes and granulocytes, both produced by the bone marrow, are involved in the mechanisms of nonspecific or innate defense (it is the body’s first line of defense against aggressions generally recognized as dangerous); they have the characteristic of containing lysosomes rich in enzymes capable of digesting foreign material (microorganisms, damaged cells and cell fragments). The products of this breakdown process act as chemotactic substances, capable of attracting and activating other granulocytes and monocytes to deal with the problem.
THE lymphocytes they are instead produced in the lymph nodes, spleen and thymus, and intervene in the specific defense mechanisms: they are custodians of immunological memory and, through the production of antibodies (humoral immunity linked to B lymphocytes), or the action of specific membrane receptors (cellular immunity mediated by T lymphocytes), eliminate substances and foreign bodies recognized as dangerous thanks to presence of antigens (foreign protein substances present on the surface of a microorganism or allergen).

If the lymphocytes are stimulated by an antigen, the B lymphocytes transform into plasma cells, which synthesize and release antibodies (immunoglobulins); these antibodies are transported by the blood to the area of ​​infection, where they bind to the invaders, labeling them as dangerous in the eyes of the other components of the immune system, which will intervene accordingly.

Because they measure themselves

The analysis of granulocytes is part of the complete blood count with leukocyte formula, performed as part of routine tests to evaluate the patient’s health status.
The counting and morphological analysis of granulocytes is also performed as a support for the diagnosis of pathological conditions, which can affect this type of white blood cell, such as:

• Infections caused by bacteria, viruses, fungi or parasites;
• Inflammations;
• Allergies;
• Neoplasms;
• Immune disorders (acquired or non-acquired immunodeficiencies, autoimmune diseases, etc.);
• Poisoning from drugs or chemicals.

The analysis of granulocytes also allows you to:

• Monitor the progression of specific pathologies;
• Check the body’s response to various treatments, especially if the therapeutic protocol (such as radiotherapy and chemotherapy) tends to damage white blood cells and/or compromises the function of the bone marrow.

Normal values

The values ​​of various types of white blood cells are counted during a blood test known as Leukocyte formula.

Below we report the reference values, remembering that the normal ranges may vary slightly based on the laboratory carrying out the analysis and the type of reference population (sex, age, etc.).

NOTE: between the two values ​​(percentage and absolute) it is more important to consider the absolute one; in fact, evaluating only the percentage value risks misinterpreting the result of the leukocyte count.

For example, the percentage value could be excessive or too low even when it is absolutely normal in absolute terms; this can happen due to the simultaneous increase or reduction of another category of leukocytes, with a change in the absolute number of white blood cells.
In some reports the absolute values ​​of the leukocyte types may be indicated with different units of measurement; it is therefore necessary to carry out the necessary conversions to return to the units of measurement shown in the table.

High Granulocytes – Causes

HIGH NEUTROPHIC GRANULOCYTES (Neutrophilia)

HIGH EOSINOPHIC GRANULOCYTES (Eosinophilia)

HIGH BASOPHILIC GRANULOCYTES (Basophilia)

Low Granulocytes – Causes

LOW NEUTROPHIC GRANULOCYTES (Neutropenia)

LOW EOSINOPHIC GRANULOCYTES (Eosinophilopenia)

LOW BASOPHILIC GRANULOCYTES (Basophilopenia)

How they are measured

For the examination of granulocytes, it is sufficient to undergo a complete blood count (blood count), where the red blood cell and platelet counts will also be analyzed, the hematocrit and corpuscular indices will be calculated.

During the exam, a blood sample is taken from the patient from a vein in the arm, usually in the morning and on an empty stomach.
The counting can be done automatically by electronic counters or by observation under an optical microscope (blood smear).

Online converter

In the previous chapter we saw that to evaluate whether there is a real increase (or decrease) in a leukocyte type, it is necessary to consider not so much the relative percentage, but rather the absolute value of that leukocyte subpopulation.

If this last data is not included in the report, it is still possible to calculate it starting from the total number of leukocytes and the relative percentage of the five types of white blood cells: simply multiply the percentage of the type of leukocyte considered by the total number of white blood cells and divide the result times 100, or more simply entrust the calculation to this automatic converter.

Preparation

To undergo the blood test useful for the evaluation of granulocytes, it is necessary to abstain from food and drink for at least 8-10 hours.

The general practitioner who prescribes the tests will still be able to provide useful information in the case.

Interpretation of Results

In making the diagnosis, the doctor will consider the degree of increase or decrease in each type of granulocyte, as well as evaluating the individual’s symptoms and medical history.

Possible causes of altered values