Monocytes - Kresser Institute Membership Site

Marker Name: Monocytes

REFERENCE RANGES FOR MONOCYTES:

Laboratory reference range:
Relative 2–12%
Absolute 0.1–0.9 x10³/µL

Functional reference range:
Relative 4–7%
Absolute N/A

DESCRIPTION:

Monocytes are one of the two main types of agranulocytes, along with lymphocytes. The prototypical monocyte is larger than other white blood cells and has a single, lobed, kidney-shaped nucleus.¹ Normally, monocytes make up less than 10 percent of circulating white blood cells. While monocytes are produced from precursor cells in the bone marrow, approximately half of all monocytes can be found in the spleen at any one time. Monocytes play important roles in inflammation and in the innate immune system response pathogens, but they may also exacerbate certain inflammatory diseases, such as atherosclerosis.²

In the absence of infection or inflammation (i.e., steady state), monocytes do not proliferate; rather, they maintain a stable number in various pools throughout the body.² When monocytes encounter an antigen, they activate, signal to other monocytes using chemokines, and rapidly move from the blood to the tissues.³ During inflammation, monocytes can become macrophages or inflammatory dendritic cells.³ These cells can phagocytose, or consume microbes.⁴ Macrophages, and especially dendritic cells, help coordinate the actions of B and T lymphocytes.⁴ Endogenous factors called lipid mediators can stop acute inflammation by monocytes and macrophages.^5,6

Monocytosis is an abnormally high number of monocytes in the circulation. Monocytosis is either reactive or clonal. Reactive monocytosis occurs during certain stresses encountered by the affected individual, such as chronic infection, inflammatory diseases, and severe trauma.⁷ Clonal monocytosis reflects a cancerous state and is most often associated with the myelomonocytic or monocytic subtypes of acute myeloid leukemia.^8,9

An abnormally low number of circulating monocytes is called monocytopenia. Until recently, monocytopenia was not believed to be a distinct entity.¹⁰ Monocytopenia was considered in the context of neutropenia or general leukopenia. However, people with mutations in the GATA2 gene may be chronically deficient in or completely lack monocytes. These individuals are particularly susceptible to certain infections, such as nontuberculous mycobacterial infection, molluscum contagiosum, and Epstein-Barr virus infections.^11,12 People with the GATA2 mutation are also prone to develop acute myelogenous leukemia and chronic myelomonocytic leukemia.¹³

A monocyte count is reported as part of a CBC with differential. The standard differential is an automated count of the main leukocyte types: monocytes, lymphocytes, eosinophils, basophils, and neutrophils.¹⁴

PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS:

High in:^1,7,8,15-17

Acute stress
Myeloproliferative disorders
Chronic infections
- Tuberculosis
- Brucellosis
- Bacterial endocarditis
- Typhoid
- Protozoal infections
- Rickettsial diseases
- Malaria
Noninfectious inflammation
- Rheumatoid arthritis
- Inflammatory bowel disease
- Temporal arteritis
- Systemic lupus erythematosus
- Collagen vascular disease
Hematologic cancers
- Hodgkin lymphoma
- Chronic myeloid leukemia
- Acute myeloid leukemia (myelomonocytic, monoblastic)

Low in:^13,18-21

Mutations of the hematopoietic transcription factor gene GATA2
Infection
Aplastic anemia
Severe thermal injury
Hematologic cancers
- Acute myeloid leukemia
- Hairy cell leukemia
- Chronic lymphocytic leukemia
Drugs (e.g., chemotherapy, corticosteroids)

FUNCTIONAL RANGE INDICATIONS:

High in:

Same as conventional indications
Inflammation

Low in:

Same as conventional indications

References: