Monocytes: Normal, High & Low Levels

How Monocytes Function in the Body

Monocytes: Normal, High & Low Levels

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Monocytes are a type of white blood cell. other white blood cells, monocytes are important in the immune system’s ability to destroy invaders, but also in facilitating healing and repair.

Monocytes are formed in the bone marrow and are released into peripheral blood, where they circulate for several days.

They comprise about 5% to 10% of the circulating white blood cells in healthy individuals.

Monocytes are probably best known for their role in serving as something akin to reserve forces in the military.

Some of them may be called up if needed, to form the precursors of two other types of white blood cells: tissue macrophages and dendritic cells.

But monocytes also have other roles in infection and disease, some of which have nothing to do with tissue macrophages and dendritic cells.

Until recently, the main role of monocytes was considered to be sensing the environment and replenishing the pool of tissue macrophages and dendritic cells, as needed.

Now it is known that different subsets of monocytes have different markers or protein tags on the outside, and these subsets may also behave differently. Three different kinds of human monocytes are now described:

  • Classical monocytes account for about 80 percent of the total monocyte population.
  • The remaining 20 percent can be classified by their protein tags as non-classical monocytes and intermediate monocytes

When it comes to the different kinds of monocytes and how they function in the immune system, researchers are still working out the details, and much more is currently known about mouse monocytes than human monocytes.

The terms “inflammatory” and “anti-inflammatory” are also used to describe human monocytes, the particular protein tags, or receptors, found on the outside of these cells.

It is not yet certain in humans, however, what proportion of monocytes are mobile enough to go in and tissues, and evidence suggests there may be kinds of monocytes that can engulf and digest, or phagocytize, invaders but without actively promoting inflammation.

A good number of human monocytes are believed to migrate into tissues throughout your body where they may reside or give rise to macrophages that perform essential functions to fight infection and clean up dead cells. The spleen has all major types of “mononuclear phagocytes,” including macrophages, dendritic cells, and monocytes. In this way, the spleen can be an active site for the innate immune system.

Innate immunity refers to the immunity you are born with, not the more targeted immunity you might develop after, say, a vaccine or after recovering from an infectious illness. The innate immune system works through different mechanisms, including phagocytosis and inflammation.

Macrophages can engage in phagocytosis, a process by which they engulf and destroy debris and invaders. They can also “retire” any old, worn-out red blood cells in this way.

Macrophages in the spleen help by cleaning the blood of debris and old cells, but they also may help the T-lymphocytes recognize foreign invaders. When this happens, it is called antigen presentation.

This last part, antigen presentation, is where the innate immune system ends and where the acquired or learned immune response to a specific foreign invader begins.

From above, we know that some monocytes transform into macrophages in the tissues that are Pac-Man, gobbling up bacteria, viruses, debris, and any cells that have been infected or are sick.

Compared to the specialized immune infantry (the T-cells), macrophages are more immediately available to recognize and attack a new threat.

They may simply be sitting in their usual favorite spots, or they may quickly migrate to a site of inflammation where they may be needed to fight an infection.

Other monocytes transform into dendritic cells in the tissues, where they work with the T lymphocytes. Macrophages can also present antigens to T-cells, but dendritic cells have traditionally been considered quite the specialists when it comes to this task.

They accumulate debris from the breakdown of bacteria, viruses, and other foreign material and present it to the T-cells so they can see it and form an immune response to the invaders. macrophages, the dendritic cells are able to present antigens to T-cells in a certain context, as if to say, “Hey look at this, do you think we should be doing more about this?”

When you have a complete blood count (CBC) blood test done with a differential count, the white blood cell monocytes are counted and the number is reported, as well as what percentage of total white blood cells are monocytes.

  • An increase in monocytes may be the result of an infection by a bacteria, fungus, or virus. It can also be a response to stress. In some cases, elevated monocyte counts may be due to a problem with the way your body makes new blood cells, and in certain cases, the excess is due to a malignancy, such as certain types of leukemia.
  • Low levels of monocytes may be seen after chemotherapy, usually because your overall white blood cell count is low.

In humans, monocytes have been implicated in a number of diseases including microbial infection, shock, and rapidly emerging organ injuries, osteoporosis, cardiovascular disease, metabolic diseases, and autoimmune diseases. However, how it is that different kinds of monocytes behave in various human diseases is still an area of active research.

Listeria monocytogenes is a species of bacteria that can cause listeriosis, a notorious foodborne illness. Listeria precautions are one of several given during pregnancy, since Listeria can cause meningitis in newborns as well as pregnancy loss; pregnant mothers are often advised not to eat soft cheeses, which may harbor Listeria.

It turns out that monocytes can help fight infection, but they can also become “Trojan horses,” by transporting bacteria into the brain, and that is a concern with Listeria. The Listeria gets inside the monocytes, but then the monocytes are unable to kill the bacteria and they multiply.

The line of cells that gives rise to monocytes can become disordered and multiply control. Acute monocytic leukemia, or “FAB subtype M5” using one classification system, is one of the forms of acute myelogenous leukemia. In M5, more than 80% of the disordered cells are monocytes.

In chronic myelomonocytic leukemia, or CMML, there are increased numbers of monocytes and immature blood cells in the bone marrow and circulating in the blood.

CMML has features of two different blood disorders, so it is categorized using the World Health Organization classification system as an combination entity: myelodysplastic syndrome/myeloproliferative neoplasm, or MDS/MPN.

It can progress to acute myeloid leukemia in about 15% to 30% of patients.

Researchers are finding that monocytes may have undesirable actions in relation to tumors and cancerous behaviors of the lymphocyte-white blood cell family (these diseases are known as lymphoproliferative diseases).

The presence of macrophages and their activities in tumors have been associated with enabling the tumor cells to build a blood supply and to invade and travel through the bloodstream. In the future, this finding might lead to therapy that targets macrophages to prevent metastasis and tumor growth.

For a variety of illnesses, some clinicians are beginning to use the absolute monocyte count as an indicator of risk, or a worse prognosis before treatment.

An increased number of monocytes above a certain threshold is associated with a poorer outcome in patients with T-cell lymphomas and Hodgkin disease.

 The lymphocyte-to-monocyte ratio may also help identify high-risk patients in diffuse large B-cell lymphoma and untreated metastatic colorectal cancer.



Monocytes: Normal, High & Low Levels

Monocytosis is defined as an absolute monocyte count greater than 2SD above the mean for the patient population. Typically, this represents a monocyte count greater than 800 per microliter in adults.

Monocyte counts may be significantly higher in children (e.g., up to 3000 per microliter), and age-specific normals should be used to determine if the monocyte count is truly elevated in a younger patient.

Note that a finding of monocytosis should not be a differential count reported in percentages.

Depending on the total white cell count (WBC) an elevation in the percentage of monocytes may reflect either true monocytosis (high WBC), lymphopenia (normal or low WBC), or neutropenia (normal or low WBC).

Therefore, the diagnosis of monocytosis should be an absolute monocyte count either provided directly by the performing laboratory or calculated (AMC = WBC x % monocytes x 100).

Monocytosis is most commonly associated with sub-acute or chronic infections (e.g., endocarditis, tuberculosis, syphilis, protozoan, or rickettsial infections), collagen vascular disorders, bone marrow recovery, granulomatous inflammation (e.g., sarcoidosis), and hematologic disorders.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

In a patient without an apparent clinical cause or a history of monocytosis, it is probably most appropriate to simply repeat a complete blood count (CBC) on a new sample to confirm that monocytosis is truly present.

Although uncommon, sample mislabeling and laboratory error may result in an erroneous or transient monocytosis that may simply disappear on repeat testing. Additionally, monocyte numbers may increase 50-100% after exercise, ly secondary to demargination.

The increase tends to parallel the intensity and duration of the exercise.

If monocytosis is present on repeat testing, the next step is to thoroughly review the remainder of the CBC for other abnormalities and ask the laboratory to review a well-made peripheral smear for red cell, white cell, and platelet morphology.

CBC should be reviewed; in particular, look for any of the following: leukocytosis, anemia, polycythemia, thrombocytopenia, thrombocytosis, or high or low mean corpuscular volume (MCV).

Review the peripheral smear. For general assessment, look for evidence of red cell or platelet clumping that may cause spurious leukocytosis and/or monocytosis.

Leukocyte morphology includes presence of immature granulocytes, monocytes, or blasts (leukemoid reaction, leukoerythroblastosis, leukemia, myloproliferastive disorder); monocyte vacuolization, hypergranularity, phagocytosed organism, or cells; neutrophil hypersegmantation (early recovery of vitamin deficiency, myelodysplasia); and pseudo-Pelger-Huet cells (myelodysplasia).

Red cell morphology includes nucleated red cells (marrow infiltration, leukoerythroblastosis, marrow recovery); dysplastic forms (myelodysplasia); intracellular organisms (Malaria sp., Babesia sp.); schistocytes (TTP, HUS, DIC, endocarditis, other microangiopathic processes); sickle cells (HbSS as a cause of asplenia); and marked polychromasia (marrow recovery).

Platelet morphology includes large platelets (marrow recovery) and abnormal platelet shape or granulation (myelodysplasia).

A thorough history and physical exam may be useful in identifying the cause of monocytosis.

History should include:

hematologic disorders or treatments that suppress bone marrow

collagen vascular disorders, such as rheumatoid arthritis and polymyositis

gastrointestinal (GI) disorders, such as sprue, ulcerative colitis, and Crohn’s disease

solid tumors


evidence of or exposure to tuberculosis, rickettsia, or protozoan parasites

full medication history, especially marrow suppressants

evidence of chronic infection, weight loss, fevers, or night sweats


Physical examination should include:

fever, adenopathy

splinter hemorrhages, cardiac murmur, or other evidence of endocarditis

splenomegaly or evidence of splenectomy

skin lesions suggesting sarcoidosis (Erythema nodosum, Lupus pernio)

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?

Monocytosis may be seen in patients receiving cytokines (GM-CSF, M-CSF) TNF-alpha or drugs that increase levels of IL- 3, IL-6, or IL-1. It has also been described in patients taking Olanzapine, allopurinol, corticosteroids, and Griseofulvin.

Additionally, monocytosis may be a harbinger of early marrow recovery after marrow suppression from drugs or other causes.

What Lab Results Are Absolutely Confirmatory?

Absolute confirmation of monocytosis is provided by repeat CBC with absolute differential count.

Differential Blood Count: Reference Range, Interpretation, Collection and Panels

Monocytes: Normal, High & Low Levels

Differential blood count can be performed by the following 2 methods:

  • Automated differential blood count: Automated hematology instruments using multiple parameters and methods (such as fluorescence flow cytometry and impedance) are used to count and identify the 5 major white blood cell types in blood (so-called 5-part differential count): neutrophils, lymphocytes, monocytes, eosinophils and basophils. [4, 5]
  • Manual differential blood count: This is performed by visual examination of peripheral blood smear (blood films) by trained personnel. [4]

The automated differential blood count is less time-consuming and less expensive than routine examination of blood smear. With the automated technique, thousands of white blood cells can be examined, whereas typically 100-200 white blood cells are examined by visual examination. [6]

Differential blood count is primarily needed in the 2 following reasons. [2]

  • To look for quantitative abnormalities in morphologically normal WBC population such as in the diagnosis of infectious or allergic diseases and for therapeutic monitoring of cytotoxic or myelotoxic drugs (This requires a high level of precision and accuracy [ie, ability to provide consistent and correct results]).
  • To look for morphologic abnormalities of white blood cells (eg, when circulating abnormal white blood cell population such as immature or atypical cells are suspected for diagnostic or monitoring reasons; this requires a high level of clinical sensitivity, [ie, ability to identify all patients who have circulating abnormal WBCs]).

Accuracy, precision, and clinical sensitivity

The automated differential blood count provides a high level of accuracy and precision (correct and consistent results) for quantification and identification of normal white blood cells; however, this method is not sensitive at identifying abnormal or immature cells and is not able to accurately identifying and classifying all types of white blood cells. To overcome this problem, most automated analyzers will flag samples with possible abnormal white blood cell populations, indicating the need for peripheral smear examination to be examined by trained personnels to identify abnormal cells. [6, 2]

Monocyte count and basophil count are the most difficult population to count and have a low level of precision and accuracy. Moreover, automated analyzers tend to underestimate the basophil count during true basophilia. [2]

False negative

Both automated and manual methods may not detect small numbers of abnormal cells. The false negative rate for detection of abnormal cells varies from 1-20%, depending on the instrument and the detection limit desired (1-5% abnormal cells). The most difficult for both automated instruments and visual examination by human is identification of lymphoma cells and reactive lymphocytes. [5]

Band neutrophils and immature granulocytes (IGs)

The value of reporting band neutrophils is questionable. The measurement of the immature cells of the myeloid lineages, specifically “band,” has been considered clinically useful in the diagnosis of infections, especially neonatal sepsis. [7]

However, band neutrophils cannot be enumerated by automated analyzers and are reported together with segmented neutrophils as absolute neutrophil counts (ANC), which are used to defined neutropenia or neutrophilia.

Identification of band neutrophils by visual examination (manual differential blood count) is neither precise nor consistent, as a high variability of morphologic classification or quantification of band neutrophils exists due to interobserver variability.

Some, therefore, advocated ceasing quantitative reporting of band neutrophils. [5, 2] The extended differential count includes reporting immature granulocytes (IG) can be used alternatively to help diagnosis neonatal sepsis. [2] For further reading, see Interpretation.


Monocytes: Normal, High & Low Levels

Monocytes: Normal, High & Low Levels

Monocytes are the largest of all white blood cells and play an important role in the defense against germs and in inflammation. Read on to learn about the normal range of these cells and the health implications of abnormal levels.

The Front Lines of Your Immunity

Monocytes are the largest type of white blood cell. Approximately 2 to 10% of white blood cells are monocytes [1].

These immune cells circulate in the blood for several days before they enter the tissues, where they become macrophages or dendritic cells [1, 2].

Monocytes protect against viral, bacterial, fungal, and protozoal infections. They kill microorganisms, ingest foreign particles, remove dead cells, and boost the immune response [3, 1, 4, 2].

However, they can also be involved in the development of inflammatory diseases arthritis and atherosclerosis. In this post, we’ll take a closer look at how monocytes work and how they may be implicated in disease [5, 6, 7].


All blood cells originate from common parent cells called hematopoietic stem cells. In adults, blood cells are produced mainly in the bone marrow; this process is called hematopoiesis. The process of monocyte production in particular is called myelopoiesis [8, 9].

Myelopoiesis is subject to a complex regulatory system, including such factors as:

  • Transcription factor SPI1 [10, 11, 12, 13].
  • Cytokines: SCF (stem cell factor), GM-CSF (granulocyte-macrophage-colony-stimulating factor), M-CSF (macrophage colony-stimulating factor, CSF1), IL-3, IL-6, and IFN-gamma [14, 15, 16, 17].

After Monocytes Fulfill Their Job, What Happens Next?

Monocytes live for an average of three days before undergoing apoptosis (programmed cell death). They live longer during periods of high inflammation; once inflammation resolves, cell death occurs [18, 19].

Monocyte Reference Ranges

The normal ranges for monocytes may be reported in a few different units. Ask your doctor to help you interpret your lab test results. The normal ranges are:

  • 0.2 – 0.8 x109/L
  • 200 – 800 / microL
  • 1 – 10%

Monocyte counts within these ranges are associated with reduced rates of:

  • Viral, bacterial, and fungal infections [20]
  • Heart Disease [21]
  • Obesity [22]
  • Diabetes [22]
  • Death (mortality) [23]

Again, it’s important to talk to your doctor if you think something may be wrong. Other suggested marker tests you may want to ask about if your monocytes are the optimal range include:

  • White blood cell count
  • Neutrophils
  • Eosinophils
  • Lymphocytes
  • Basophils

High Levels of Monocytes (Monocytosis)

Monocytosis is a condition in which the number of monocytes circulating in the blood is increased to more than 0.8×109/L in adults.

Conditions Associated with Monocytosis

  • Blood disorders (myelodysplastic disorder, acute monocytic, chronic myelomonocytic leukemia, Hodgkin and non-Hodgkin lymphoma) [24, 25, 26]
  • Infections (tuberculosis, viral infections, bacterial endocarditis, brucellosis, malaria, syphilis) [27, 28, 29, 30, 31, 32]
  • Autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease) [33, 34, 35]
  • Sarcoidosis [36]
  • Cancers (ovary, breast, rectum) [27, 37]
  • Heart attack [27, 38]
  • Appendicitis [39]
  • HIV infection [27, 40]
  • Depression [41]
  • Childbirth [42, 43]
  • Obesity [44]
  • Severe pneumonia [45]
  • Alcoholic liver disease [46]

Causes shown here are commonly associated with this symptom. Work with your doctor or other health care professional for an accurate diagnosis.

Symptoms and Causes

Monocytosis most commonly occurs during and after chronic inflammation or infection [23].

However,several other conditions can also be associated with monocytosis, such as heart disease, depression, diabetes, and obesity [21, 22, 47].

The conditions most commonly associated with high monocyte levels are:

  • Chronic (long-term) inflammation [23]
  • Infections, such as tuberculosis, malaria, and syphilis [48, 49, 50]

High monocyte levels may also be linked to:

  • Autoimmune diseases, such as lupus, rheumatoid arthritis, and IBD [35, 33, 34]
  • Leukemias, such as chronic myelomonocytic leukemia, and juvenile myelomonocytic leukemia [51, 52]
  • Cancer [53]
  • Depression [41]
  • Obesity [54]

Few symptoms are considered to be caused by monocytosis itself. Instead, according to many researchers, symptoms arise from the diseases associated with monocytosis [22]. These symptoms include:

  • Fever [55]
  • Pain [56]
  • Swelling [55]

Low Levels of Monocytes (Monocytopenia)

In monocytopenia, the number of monocytes circulating in the blood is decreased to less than 0.2×109/L in adults. Monocytopenia itself does not appear to produce symptoms, and patients usually only show symptoms related to an associated condition. Such symptoms may include fatigue and fever [20, 57].

Conditions Associated with Monocytopenia

  • Aplastic anemia [58]
  • Leukemia (hairy-cell leukemia, chronic lymphocytic leukemia) [59]
  • Chemotherapy [60]
  • MonoMAC syndrome (monocytopenia and Mycobacterium Avium Complex syndrome) [61]
  • Severe burn injuries [62]
  • Rheumatoid arthritis [63]
  • Systemic lupus erythematosus [64]
  • HIV infection [65]
  • Vitamin B12 deficiency [66]
  • Corticosteroid therapy (transient monocytopenia) [67]
  • Administration of INF-alpha and TNF-alpha [68]
  • Radiation therapy [69]


Monocytes are the largest of the white blood cells. They kill microbes, recycle old cells, and boost immunity. People with monocyte levels within the normal range (0.2 – 0.8 x109/L) tend to develop fewer infections and chronic diseases.

The most common causes of high monocytes (monocytosis) are chronic infections and inflammation. In turn, high monocytes can worsen inflammation and clog your blood vessels. Many health conditions can also cause low monocyte levels (monocytopenia), including autoimmune diseases and nutrient deficiencies.

Having low monocytes may reduce your risk of heart disease but makes you more prone to infections and blood disorders.

Further Reading

Have you recently had your monocyte count tested? Want to learn about what your results mean? Check out these posts:

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Blood differential test

Monocytes: Normal, High & Low Levels

Differential; Diff; White blood cell differential count

The blood differential test measures the percentage of each type of white blood cell (WBC) that you have in your blood. It also reveals if there are any abnormal or immature cells.

Basophils are a specific type of white blood cell. These cells are readily stained with basic dyes (this is where the name comes from). Note the dark grains inside the cellular fluid (cytoplasm) of this basophil.

Basophils make up only a small portion of the number of white blood cells but are important parts of the body's immune response.

They release histamine and other chemicals that act on the blood vessels when the immune response is triggered.

Blood transports oxygen and nutrients to body tissues and returns waste and carbon dioxide. Blood distributes nearly everything that is carried from one area in the body to another place within the body.

For example, blood transports hormones from endocrine organs to their target organs and tissues. Blood helps maintain body temperature and normal pH levels in body tissues.

The protective functions of blood include clot formation and the prevention of infection.

A blood sample is needed.

A laboratory specialist takes a drop of blood from your sample and smears it onto a glass slide. The smear is stained with a special dye, which helps tell the difference between various types of white blood cells.

Five types of white blood cells, also called leukocytes, normally appear in the blood:

  • Neutrophils
  • Lymphocytes (B cells and T cells)
  • Monocytes
  • Eosinophils
  • Basophils

A special machine or a health care provider counts the number of each type of cell. The test shows if the number of cells are in proper proportion with one another, and if there is more or less of one cell type.

No special preparation is necessary.

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

This test is done to diagnose an infection, anemia, or leukemia. It may also be used to monitor one of these conditions, or to see if treatment is working.

The different types of white blood cells are given as a percentage:

  • Neutrophils: 40% to 60%
  • Lymphocytes: 20% to 40%
  • Monocytes: 2% to 8%
  • Eosinophils: 1% to 4%
  • Basophils: 0.5% to 1%
  • Band (young neutrophil): 0% to 3%

Any infection or acute stress increases your number of white blood cells. High white blood cell counts may be due to inflammation, an immune response, or blood diseases such as leukemia.

It is important to realize that an abnormal increase in one type of white blood cell can cause a decrease in the percentage of other types of white blood cells.

An increased percentage of neutrophils may be due to:

  • Acute infection
  • Acute stress
  • Eclampsia (seizures or coma in a pregnant woman)
  • Gout (type of arthritis due to uric acid buildup in the blood)
  • Acute or chronic forms of leukemia
  • Myeloproliferative diseases
  • Rheumatoid arthritis
  • Rheumatic fever (disease due to an infection with group A streptococcus bacteria)
  • Thyroiditis (a thyroid disease)
  • Trauma
  • Cigarette smoking

A decreased percentage of neutrophils may be due to:

An increased percentage of lymphocytes may be due to:

A decreased percentage of lymphocytes may be due to:

  • Chemotherapy
  • HIV/AIDS infection
  • Leukemia
  • Radiation therapy or exposure
  • Sepsis (severe, inflammatory response to bacteria or other germs)
  • Steroid use

An increased percentage of monocytes may be due to:

  • Chronic inflammatory disease
  • Leukemia
  • Parasitic infection
  • Tuberculosis, or TB (bacterial infection that involves the lungs)
  • Viral infection (for example, infectious mononucleosis, mumps, measles)

An increased percentage of eosinophils may be due to:

An increased percentage of basophils may be due to:

A decreased percentage of basophils may be due to:

  • Acute infection
  • Cancer
  • Severe injury

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Multiple punctures to locate veins
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

Chernecky CC, Berger BJ. Differential leukocyte count (diff) – peripheral blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:440-446.

Hutchison RE, Schexneider KI. Leukocytic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 33.

Last reviewed on: 1/29/2019

Reviewed by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.


What Is Chronic Myelomonocytic Leukemia?

Monocytes: Normal, High & Low Levels

Chronic myelomonocytic leukemia (CMML) starts in blood-forming cells in the bone marrow and invades the blood.

Cells in nearly any part of the body can become cancer and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?

Normal bone marrow

Bone marrow is found inside certain bones such as the skull, ribs, pelvis, and spine. It's made up of blood-forming cells, fat cells, and supporting tissues that help the blood-forming cells grow.

A small fraction of the blood-forming cells are a special type of cell known as stem cells. Stem cells are needed to make new cells.

When a stem cell divides, it makes 2 cells: one cell that stays a stem cell and another cell that can keep changing and dividing to make blood cells.

There are 3 types of blood cells: red blood cells, white blood cells, and platelets.

Red blood cells pick up oxygen in the lungs and carry it to the rest of the body. These cells also bring carbon dioxide back to the lungs. Having too few red blood cells is called anemia. People with anemia can look pale and feel tired and weak. Severe anemia can cause shortness of breath.

White blood cells (also called leukocytes) are important in fighting infection.

  • Lymphocytes are immune cells in the bone marrow, the blood, and in lymph nodes. Some kinds of lymphocytes make the antibodies that help your body fight germs. Other kinds directly kill invading germs by making toxic substances that damage the cells.
  • Granulocytes are white blood cells that destroy bacteria. They contain granules that are made up of enzymes and other substances which can destroy germs that cause infections. In the bone marrow, granulocytes develop from young cells called myeloblasts. The most common type of granulocyte is the neutrophil; which is crucial in fighting bacteria. Other types of granulocytes are basophils, and eosinophils. When the number of neutrophils in the blood is low, it is called neutropenia. This can lead to severe infections.
  • Monocytes are related to the granulocyte family. They also help protect you against bacteria. The early cells in the bone marrow that turn into monocytes are called monoblasts. When monocytes leave your bloodstream and go into tissue, they become macrophages. Macrophages can destroy germs by surrounding and digesting them. They're also important in helping lymphocytes recognize germs and start making antibodies to fight them.

Platelets are thought of as a type of blood cell, but they're really small pieces of a cell. They start as a large cell in the bone marrow called the megakaryocyte.

Pieces of this cell break off and enter your bloodstream as platelets, which you need for your blood to clot. Platelets plug up damaged areas of blood vessels caused by cuts or bruises.

If you have a shortage of platelets (a condition called thrombocytopenia) you can bleed and bruise a lot.

Features of chronic myelomonocytic leukemia

  • People with CMML may have shortages of some blood cells, but a main problem is too many monocytes. (at least 1,000 per mm3). Often, the monocyte count is much higher, causing their total white blood cell count to become very high as well.
  • Usually there are some abnormal cells, called blasts, in the bone marrow. The amount of blasts in CMML is below 20%.
  • Many people with CMML have enlarged spleens (an organ that lies just below the left rib cage).
  • About 15% to 30% of people with CMML go on to develop acute myeloid leukemia.
  • The DNA inside the abnormal cells does not have certain changes in the genes called BCR/ABL (Philadelphia chromosome), or PDGFRA and PDGRFRB. For more information about these gene changes, see How Is Chronic Myelomonocytic Leukemia Diagnosed?

Since CMML has features of both a myelodysplastic syndrome and myeloproliferative neoplasm, experts created a new category for it: myelodysplastic/myeloproliferative neoplasm (myelo — bone marrow, proliferative — excessive growth, dysplastic — abnormal looking).CMML is the most common disease in this group. Much less common diseases in this group are atypical chronic myeloid leukemiaand juvenile myelomonocytic leukemia. All of these diseases produce a lot of abnormal blood cells.

Chronic myeloid leukemia is an example of a myeloproliferative neoplasm where there' is an over-production of white blood cells.


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Monocytes: Normal, High & Low Levels

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