Leukocytosis: Definition, Causes, Classification, Symptoms, Diagnosis, Treatment and Prevention

It refers to an increase in the total number of white blood cells due to any cause.

Leukocytosis is a condition in which a white blood cell count is greater than 11,000 per mm 3 (11 × 10 9 per L), a higher number than normal.

Leukocytosis, a common laboratory finding, is most often due to relatively benign conditions (infections or inflammatory processes).

Much less common but more serious causes include primary bone marrow disorders .

The normal reaction of the bone marrow to infection or inflammation leads to an increase in the number of white blood cells, predominantly polymorphonuclear leukocytes and less mature cell forms (the “shift to the left”).


It is usually caused by an increase in the number of granulocytes (especially neutrophils ), some of which may be immature (myelocytes).

Most of the time, leukocytosis is the result of the presence of an infection, usually caused by pyogenic (pus-producing) organisms such as streptococcus, staph, gonococcus, pneumococcus, or meningococcus.

White blood cell counts of 12,000 to 20,000 per cubic millimeter during infections are not unusual.

As the number of cells increases, the proportion of immature cells generally increases.

Perhaps due to the demands of the leukocyte-producing tissues in the bone marrow it has increased to the point where there are insufficient numbers of mature cells to supply the circulation.

As the infection subsides, the number of younger forms and the total white blood cell count decrease and eventually return to normal.

During the repair period after an inflammatory reaction, monocytes may increase in number, and later lymphocytes will become more numerous.

Certain types of infection are characterized early on by an increase in the number of small lymphocytes not accompanied by increases in monocytes or granulocytes. Lymphocytosis is usually viral in origin.

Moderate degrees of lymphocytosis are found in certain chronic infections such as tuberculosis and brucellosis.

Mononucleosis, caused by the Epstein-Barr virus, is associated with the appearance of unusually large lymphocytes (atypical lymphocytes).

These cells represent part of the complex defense mechanism against the virus, and disappear from the blood when the attack of infectious mononucleosis subsides.

The stress physical, seizures, anesthesia or excessive stress, work stress, emotional stress can also raise white blood cell count.

Medications commonly associated with leukocytosis include corticosteroids , lithium, and beta agonists.

Classification of leukocytosis

From a practical point of view, leukocytosis is traditionally classified according to the component of white cells that contribute to an increase in the total number of white blood cells.

By dividing leukocytosis based on causes, it can be applied immediately for diagnostic purposes.

Leukocytosis can be caused by infection, inflammation, allergic reaction, malignancy, inherited disorders, or a variety of other causes.

Therefore, leukocytosis can be caused by:

Increased neutrophil count i.e. neutrophilia

This is an increase in white blood cells called neutrophils, which make up 40 to 60 percent of your white blood cells.

Neutrophilia is the most common type of leukocytosis associated with infection and inflammation.

Neutrophilia is also divided into 4 categories according to the mechanism of neutrophilia:

  • Increase in production.
  • Decreased outflow of the vascular space (demargination).
  • Increased mobilization of the bone marrow storage reserve.
  • Reduction of marginalization towards the fabric.

The causes of leukocytosis can be classified by type of white blood cells.

The causes of neutrophilia are:

  • Infections
  • Anything that causes long-term inflammation, including injury and arthritis.
  • Reaction to medications, such as steroids, lithium, and some inhalers.
  • Some types of leukemia.
  • A reaction to emotional or physical stress from things like anxiety, surgery, and exercise.
  • When the spleen has been removed.
  • Smoking.

Increase in lymphocyte count i.e. lymphocytosis

About 20 to 40 percent of white blood cells are lymphocytes. An increase in the number of these cells is called lymphocytosis.

This is the most common type of leukocytosis and is associated with viral infections and leukemia.

The causes of lymphocytosis are:

  • Viral infections
  • Whooping cough.
  • Allergic reactions.
  • Some types of leukemia.

Increased monocyte count i.e. monocytosis

This is the name for a high number of monocytes. These types of cells make up only about 2 to 8 percent of the white blood cell count.

Monocytosis is rare and is associated with certain infections and cancer.

The causes of monocytosis are:

  • Infections with certain things like the Epstein-Barr virus (including mononucleosis), tuberculosis, and fungi.
  • Autoimmune diseases, such as lupus and ulcerative colitis.
  • Spleen removal

Increased eosinophilic granulocyte count i.e. eosinophilia

This means that there are a large number of cells called eosinophils in the blood.

These cells make up about 1 to 4 percent of white blood cells.

Eosinophilia is also a rare type of leukocytosis and is associated with allergies and parasites.

The causes of eosinophilia are:

  • Allergies and allergic reactions, including hay fever and asthma.
  • Parasitic infections.
  • Some skin diseases.
  • Lymphoma (cancer associated with the immune system).

Increased basophilic granulocyte count i.e. basophilia

This is a high level of white blood cells called basophils. There are not many of these cells in your blood – only 0.1 to 1 percent of white blood cells.

Basophilia is rare and is associated with leukemia.

The causes of basophilia are:

  • Leukemia or cancer of the bone marrow (most often).
  • Occasionally allergic reactions.

Increase in immature cells such as blasts

A combination of any of the above may be involved.

Leukocytosis in pregnancy

Pregnant women often have higher than normal white blood cell levels.

These levels increase gradually, and in the last three months of pregnancy the white blood cell count is usually between 5,800 and 13,200 per microliter of blood.

It remains slightly above normal (around 12,700 per microliter of blood) for a time after the baby is born.


Leukocytosis itself can cause symptoms. What:

  • Vision problems
  • Fever and pain or other symptoms at the site of an infection.
  • Easy bruising, weight loss, and night sweats with leukemia and other cancers.
  • Hives, itchy skin, and rashes from an allergic skin reaction.
  • Breathing problems and wheezing from an allergic reaction in the lungs.
  • Bleeding from areas covered with mucosa, such as the mouth, stomach, and intestines.

Symptoms may not occur if the leukocytosis is related to stress or a reaction to a drug.

Diagnosis of leukocytosis

Typically, an individual has between 4,000 and 11,000 white blood cells per microliter of blood if they are not pregnant. Any higher count is considered leukocytosis.

White blood cell counts between 50,000 and 100,000 per microliter usually signify a very serious infection or cancer somewhere in the body.

A white blood cell count over 100,000 occurs most often with leukemia or other cancers of the blood and bone marrow.

There are three tests your doctor might use to determine why your white blood cell count is higher than normal:

Complete blood count with differential

This test is almost always done when your white blood cell count is higher than normal for unknown reasons.

For this test, the blood drawn from your vein is run through a machine that identifies the percentage of each type of white blood cell.

Knowing which types have higher-than-normal percentages can help your doctor reduce the possible causes of your high white blood cell count.

Peripheral blood smear

This test is done when neutrophilia or lymphocytosis is found because your doctor can see if there are too many types of white blood cells.

For this test, a thin layer of your blood sample is stained on a slide. A microscope is then used to look at the cells.

Bone marrow biopsy

Your white blood cells are made in your bone marrow and then released into your blood. When a high number of certain types of neutrophils is found in your peripheral smear, your doctor may perform this test.

Samples of your bone marrow are taken from the center of a bone, usually your hip, with a long needle and examined under a microscope.

This test can tell your doctor if there are abnormal cells or a problem with the production or release of cells from your bone marrow.


Treatment of leukocytosis is based on what causes it:

  • Antibiotics for infection.
  • Treatment of conditions that cause inflammation.
  • Antihistamines and inhalers for allergic reactions.
  • Chemotherapy, radiation, and sometimes a stem cell transplant for leukemia.
  • An adjustment in the dose of medicines if the cause is a reaction to the drug.
  • Treatment of the causes of stress and anxiety if they are present.
  • Hyperviscosity syndrome is a medical emergency treated with intravenous fluids, medications, and other methods to rapidly lower the white blood cell count. This is done to make the blood less thick and flow normally again.

Prevention of leukocytosis

The best way to prevent leukocytosis is to avoid or reduce your risk of the things that cause it. This includes:

  • Maintain a healthy lifestyle, including good hand washing to avoid infection.
  • Stay away from anything you know can trigger an allergic reaction.
  • Stop smoking to prevent smoking-related leukocytosis and lower your risk of cancer.
  • Take medications as directed if you are being treated for a condition that causes inflammation.
  • Trying to reduce the amount of stress in your life and being treated for serious anxiety or emotional problems.

Leukocytosis associated with pregnancy or in response to exercise is normal and there is nothing to worry about.