Monocytes: elevated, too low or normal value?

© Getty Images / Ed Reschke

Blood contains various cell components, including red blood cells (erythrocytes), white blood cells (leukocytes) and blood platelets (thrombocytes). The white blood cells can in turn be divided into various subgroups, including granulocytes, lymphocytes and monocytes. As a laboratory value, the monocytes are part of a complete blood count. Here you can find out what it means if the blood value is high or too low.

What are monocytes?

Monocytes are a subset of white blood cells. Their percentage of leukocytes is around two to ten percent in adults. An increase in the number of monocytes in the blood is called monocytosis, while a decrease in the number of monocytes in the blood is called monocytopenia.
With a diameter of twelve to 20 microns, the monocytes are about twice the size of the red blood cells (diameter of about 7.5 microns) and are therefore considered to be the largest cells in the bloodstream.

What develops from monocytes?

As soon as the monocytes leave the bloodstream after one to five days of life and settle in the tissue, the so-called macrophages develop from them, which, like the monocytes, are important for the immune system.

What is the function of the monocytes?

The monocytes are among the cells of the immune system and have the task of rendering pathogens harmless at an early stage. Among other things, monocytes and macrophages release messenger substances that can initiate and maintain inflammatory reactions in the body.

The development form of the monocytes in the tissue, the macrophages, also recognize foreign substances that have to be eliminated. These include, for example, pathogens such as viruses or bacteria. The macrophages remove them from the body by absorbing and eventually destroying the foreign substances. The technical term for this process is “phagocytosis”. Therefore, the macrophages can also be described as the “scavenger cells” of the blood.

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How is the laboratory value determined?

The blood value of the monocytes can be determined by taking a blood sample. A small blood count only contains the total number of white blood cells. A differential blood count, which is part of the complete blood count, is required to accurately determine the percentage of the various subgroups of leukocytes, including monocytes.

What monocyte count is normal?

The normal monocyte value depends on age. The laboratory value is given as a number of cells/µl, i.e. the number of cells per microliter of blood is recorded.

The following table shows the reference values ​​for monocytes divided into the different age groups. It should be noted that slight deviations from normal values ​​are possible in different laboratories. There are also small differences in the normal blood values ​​in men and women.

The table distinguishes between the absolute number of monocytes (abs monocytes) and the percentage of the total number of white blood cells.

Alterabsolute valuesPercentage of the total number of leukocytes
baby630 to 3,000 / .l7 bis 20 %
Kinder80 to 720 / .l1 bis 6 %
Adult200 to 800 / .l2 bis 10 %

What do elevated monocytes indicate?

An important task of the monocytes is the release of messenger substances in inflammatory reactions and in phagocytosis, i.e. the “eating” of pathogens. One reason for an increase in monocytes, i.e. for monocytosis, can therefore be an inflammatory reaction in the body.

This can occur as part of an infection with bacteria, viruses or parasites. The monocytes are needed in this context to render the pathogens harmless. In the event of an infection, the total blood value of the leukocytes is usually increased at the same time. Not only the acute infection, but also the phase of recovery after the infection can lead to monocytosis.

Accordingly, the symptoms of monocytosis can indicate an infection and include, for example, fever, body aches or swollen lymph nodes.

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In addition, the monocytes can also be slightly increased under stress.

The monocytes in the blood can also be too high in the context of autoimmune diseases. In autoimmune diseases, the body mistakenly recognizes something in the body, such as the thyroid, as foreign and needs macrophages to fight the supposed pest. In the case of the thyroid, for example, Hashimoto’s thyroiditis can increase the blood level of monocytes. Other examples of autoimmune diseases include gluten intolerance (celiac disease), the skin disease psoriasis (psoriasis) and systemic lupus erythematosus, in which any organ can be affected by the disease.

Elevated monocytes can also occur in the context of cancer. The monocyte value can also be increased in leukemia or lymph node cancer.

A natural cause of monocytosis is also pregnancy, so elevated levels are not a cause for concern.

What if you have too few monocytes?

Monocytopenia is often accompanied by a general lack of leukocytes (leukocytopenia). If the monocyte value is too low, this can have various causes. Some of the causes that can lead to monocytopenia or leukocytopenia (decrease in leukocytes) are listed below:

  • Therapy with glucocorticoids, i.e. active ingredients that are similar to the body’s own cortisone
  • Chemotherapy (cytostatics) for various types of cancer
  • Bone marrow damage, possibly caused by chemotherapy or various drugs
  • Infections can lead not only to monocytosis but also to monocytopenia
  • various blood disorders, including but not limited to aplastic anemia, in which two or all of the cell lines in the blood (erythrocytes, leukocytes and platelets) are reduced in number due to a disorder in the function of the bone marrow
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In the case of monocytopenia, the risk of contracting various infections can also increase, since the cells are an important part of the immune system and their absence weakens the immune system.

What to do if the monocyte values ​​are too high or too low?

Elevated or low monocyte levels are not a direct cause for concern. The changed values ​​are often caused by reversible processes, so the changes can be reversed. Depending on the causative agent, an infection can be treated or it can heal on its own. In the case of damaging drugs such as cytostatics as the cause of the monocytopenia, the body (and thus also the production of monocytes) can often recover after stopping these drugs.

If, on the other hand, the bone marrow is irreparably damaged, a bone marrow transplant can enable the formation of blood cells again.

Updated: 05/16/2022

Author: Silvana Schönit, student of human medicine