What Is Leukocytosis Definition Causes Types and Symptoms
The count of white blood cells (leukocytes) will vary from time to time. The highest count is being recorded in the afternoon and the lowest count is recorded in the early morning. The temporary increases in the number of leukocytes are common during pregnancy, menstruation cycle, muscular exercise, childbirth, and sometimes it gets rises even at the stress. But the abnormal changes in the count, appearance and ratio of white blood cells indicate the necessity of medical treatment. Leukocytes are a part of a human’s immune system. This is a type of immune cell that is generated from bone marrow and delivers to the blood. Leukocyte helps to fight against infections and other diseases in the body.
What is Leukocytosis?
The abnormal changes in the normal count of white blood cells are known as leukocytosis. Mild leukocytosis means markable changes in the count of leukocytes. The sudden increase of granulocytes like neutrophils, eosinophils, and basophils are common, this may because of myelocytes. The myelocytes are the immature white blood cells. The infections caused by the pyogenic organisms namely, Pneumococcus, Streptococcus, Gonococcus, Staphylococcus, and Meningococcus results in leukocytosis. The average count of leukocytes of the common man ranges from 12,000 to 20,000 per cubic millimetre. It varies for the infected person. As the number of WBC increases, the ratio of immature cells gets varies. This demands the leukocyte producing tissues present in the bone marrow to increase delivery of matured cells into the bloodstream. If the infection part controlled, the number of younger WBC get decreases and returns to the normal state. While WBC fights against inflammation repairing, the monocytes may increase and the lymphocytes will get increase simultaneously.
Leukocytosis Causes
It is possible to classify the infection at the initial stage, by analyzing the count of lymphocytes, monocytes, and granulocytes present in WBC.
Lymphocytosis usually occurs due to a viral infection. If the count of lymphocytes dramatically increased, it may be due to chronic infections such as tuberculosis and brucellosis. The Epstein-Barr virus causes mononucleosis. It results in a drastic increase in the large lymphocytes. These are also known as atypical lymphocytes. These cells represent complex defense mechanisms, It gets hidden in the bloodstream and fights against the virus mononucleosis. Infectious mononucleosis predominantly prevails in people from the age group of 10 to 30 years. They can transmit from one person to another through saliva during oral contact. The person affected by mononucleosis gets symptoms like fever, flulike symptoms, sore throat, physical discomforts, enlargement of lymph nodes and spleen..etc. The blood serum contains antibody-like sheep cells or heterophil agglutin are characteristics of the disease. But antibodies against the virus Epstein-Barr are the specific cause of the infection. The symptoms will get vary depends on the severity of the infection and the immunity of an individual. It takes few weeks to months for complete recovery. This is what is lymphocytosis granulocytopenia.
The immune response generated against the Epstein-Barr virus never gets completely eliminated from the infected person’s body. A small particle of the virus remains saved for the latent in B lymphocytes. This helps to treat chronic mild leukocytosis. In a normal person, the T lymphocytes developed from the thymus act against the latent virus to check the entry this is a natural immune response. If the natural immune response get suppresses, the immune response developed by the Epstein-Barr virus gets activated for acts against infection. This Epstein-Barr virus is a member of the herpesvirus family, The virus from this family causes diseases like cold sores, genital ulcers, and shingles. Viruses from the herpes family namely herpes simplex type 1, herpes simplex type 2, herpes zoster, and cytomegalovirus will show similar property. So, it is easy for the immunosuppressive cells to activate against it. This is known as lymphocytic leukocytosis.
If the count of monocytes gets increased in the bloodstream results in Monocytosis. These are mainly caused due to subacute bacterial endocarditis, inflammation of the lining of the heart, and malaria The severe toxic injury to the bone marrow also results in monocytes.
If the count of eosinophilic leukocytes in the bloodstream increased, it results in eosinophilic leukocytosis. The causes for eosinophilic leukocytes are allergic reactions and parasitic infractions. It is especially the characteristic of trichinosis. Trichinosis is a disorder, mainly caused due to trichina larvae. People get affected while intaking poorly cooked pork infected by trichina larvae.
Leukocytosis Symptoms
The sudden increase in the WBC count often does not show any symptoms. Although, the person who is affected by mild leukocytosis means, they will experience some common following symptoms like, body aches, fever, chills, headaches, etc.
Leukopenia
The drastic decrease in the counts of leukocytes results in leukopenia. The person affected by leukopenia has a WBC count of less than 4,000 per cubic millimetre. The neutrophilic leukocytosis causes show a sudden reduction in the number of neutrophils in WBC. This is known as neutropenia. Usually, Neutropenia does not cause any symptoms. Neutrophilic leukocytosis causes are mainly due to the bacteria. The severe sore throat, fever, and marked fatigue are the symptoms of Agranulocytosis. This is mainly due to the extreme reduction in the number of neutrophilic granulocytes or the absence of neutrophils. This neutropenia is associated with certain infections like typhoid, brucellosis HIV, measles, and some bone marrow disease.
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This image shows the slide view of blast cells of leukopenia-affected patients.
FAQs on Leukocytosis Increased White Blood Cell Count
1. What is leukocytosis?
Leukocytosis is an increase in the total number of white blood cells (WBCs) in the blood above the normal range. In adults, it is usually defined as a WBC count greater than about 11,000 cells per microliter of blood. It commonly occurs in response to infection, inflammation, stress, or bone marrow disorders and reflects activation of the immune system.
2. What causes leukocytosis?
Leukocytosis is most commonly caused by infection, but it can also result from other physiological or pathological conditions. Common causes include:
- Bacterial infections (e.g., pneumonia, appendicitis)
- Inflammation due to injury or autoimmune diseases
- Stress responses such as trauma or surgery
- Allergic reactions
- Leukemia or other bone marrow disorders
The underlying cause determines which type of white blood cell is elevated.
3. What is the normal white blood cell count?
The normal white blood cell (WBC) count in adults ranges from about 4,000 to 11,000 cells per microliter of blood. Values above this range are considered leukocytosis, while values below it are termed leukopenia. Normal ranges may vary slightly depending on age, laboratory standards, and physiological conditions such as pregnancy.
4. What are the types of leukocytosis?
The types of leukocytosis are classified based on which white blood cell type is elevated. These include:
- Neutrophilia – increased neutrophils, often due to bacterial infection
- Lymphocytosis – increased lymphocytes, common in viral infections
- Eosinophilia – increased eosinophils, seen in allergies and parasitic infections
- Basophilia – increased basophils, rare and linked to certain blood disorders
- Monocytosis – increased monocytes, associated with chronic infections
Each type reflects a specific immune response pattern.
5. How does infection lead to leukocytosis?
Infection leads to leukocytosis by stimulating the bone marrow to produce and release more white blood cells into circulation. The process occurs in steps:
- Pathogens such as bacteria or viruses invade the body.
- Immune cells release cytokines and growth factors.
- The bone marrow increases production of specific WBCs.
- More WBCs enter the bloodstream to fight the infection.
This rise in WBC count helps the body defend against harmful microorganisms.
6. What is the difference between leukocytosis and leukemia?
Leukocytosis is a temporary increase in white blood cells, whereas leukemia is a cancer of the blood-forming tissues. Key differences include:
- Leukocytosis – usually reactive, short-term, and caused by infection or stress.
- Leukemia – involves uncontrolled proliferation of abnormal WBCs in the bone marrow.
- Leukemia often produces immature or dysfunctional white cells.
Thus, leukocytosis can be a normal immune response, while leukemia is a malignant disorder.
7. What are the symptoms of leukocytosis?
Leukocytosis itself may not cause symptoms, but symptoms usually reflect its underlying cause. Common associated signs include:
- Fever in infections
- Fatigue or weakness
- Inflammation such as redness or swelling
- Unexplained weight loss in serious conditions
A complete blood count (CBC) test is typically required to detect elevated white blood cells.
8. Can stress cause leukocytosis?
Yes, physical or emotional stress can cause temporary leukocytosis by releasing stress hormones like adrenaline and cortisol. These hormones:
- Mobilize white blood cells from storage sites.
- Increase their circulation in the bloodstream.
- Prepare the body for a "fight-or-flight" response.
This type of leukocytosis is usually mild and resolves once the stress subsides.
9. How is leukocytosis diagnosed?
Leukocytosis is diagnosed through a complete blood count (CBC) test that measures the number of white blood cells in blood. Diagnosis typically involves:
- Measuring total WBC count.
- Performing a differential count to identify which WBC type is elevated.
- Evaluating clinical history and symptoms.
Further tests may be done to determine whether the cause is infection, inflammation, or a hematological disorder.
10. Why is leukocytosis important in the immune response?
Leukocytosis is important because it reflects activation of the immune system to fight infection or injury. Increased white blood cells help by:
- Engulfing pathogens through phagocytosis.
- Producing antibodies (by lymphocytes).
- Releasing inflammatory mediators.
Thus, leukocytosis is often a protective and adaptive biological response to harmful stimuli.
