What is granulocytosis? Causes, symptoms, and treatment explained

September 21, 2025 •

4 min read

Granulocytes, a specific type of white blood cell, are crucial for the body's immune defense. Granulocytosis is a medical term referring to an abnormally high number of these cells in the bloodstream, a condition that can signal an infection, inflammation, or another underlying health issue. While often a temporary response, persistent granulocytosis requires medical attention to determine its root cause.

Quick Summary

Granulocytosis is the presence of an increased number of granulocytes, a type of white blood cell, in the bloodstream, typically indicating an infection, inflammation, or a bone marrow disorder that requires investigation and treatment of the underlying cause.

Key Points

Granulocytosis is a blood condition: It refers to an abnormally high count of granulocytes, a specific type of white blood cell, in the bloodstream.
Not a disease, but a symptom: High granulocyte levels are not a disease in themselves but an indication of an underlying issue, such as an infection, inflammation, or bone marrow problem.
Diagnosis through a CBC: A complete blood count (CBC) test is the primary tool for diagnosing granulocytosis.
Treatment targets the root cause: Managing granulocytosis involves treating the medical condition causing the high cell count, not the count directly.
Variety of underlying causes: Causes can range from temporary issues like infections to more serious, chronic conditions like blood cancers.
Symptoms depend on the cause: Any symptoms experienced are typically linked to the primary medical condition, and can include fever, fatigue, or swelling.

Understanding Granulocytes and Their Role

Granulocytes are a subset of white blood cells (leukocytes) that contain small particles, or granules, filled with enzymes and proteins. These cells are an essential component of the body's innate immune system, acting as first responders to invading pathogens like bacteria, viruses, and parasites. There are three primary types of granulocytes, each with a specialized function:

Neutrophils: The most abundant type, neutrophils are phagocytes that ingest and destroy bacteria and other microorganisms. High neutrophil counts (neutrophilia) are often a sign of a bacterial infection.
Eosinophils: These cells are primarily involved in the immune response against parasites and are also elevated during allergic reactions. An increase in eosinophils is known as eosinophilia.
Basophils: The least common type, basophils contain histamine and play a significant role in allergic and inflammatory responses. High levels are called basophilia.

Causes of Granulocytosis

Granulocytosis is not a disease in itself but rather a sign that something is prompting the bone marrow to produce more granulocytes. The causes can range from temporary, self-resolving issues to more serious, chronic conditions.

Acute vs. Chronic Triggers

Infections: The most common cause, especially bacterial infections, leads to a rapid increase in neutrophils to fight the invading pathogens. Viral and parasitic infections can also cause granulocytosis.
Inflammatory Conditions: Chronic inflammation from conditions like rheumatoid arthritis or inflammatory bowel disease can lead to persistently elevated granulocyte levels.
Stress and Injury: Severe physical or emotional stress, burns, major surgery, and heart attacks can cause a temporary spike in granulocytes as part of the body's immediate response.
Medications: Certain drugs, particularly corticosteroids, can trigger an increase in granulocyte production.

Bone Marrow and Hematologic Conditions

Myeloproliferative Neoplasms (MPNs): This group of rare blood cancers, including chronic myeloid leukemia (CML), polycythemia vera, and essential thrombocythemia, can cause granulocytosis due to the uncontrolled production of blood cells in the bone marrow.
Other Cancers: Metastatic cancer can also cause elevated granulocyte levels.

Symptoms and Diagnosis

Granulocytosis itself often has no specific symptoms; any signs experienced are typically related to the underlying cause. A person might experience fever, fatigue, or swollen glands if the cause is an infection. In cases of underlying CML, symptoms can include fatigue, night sweats, pale skin, and abdominal discomfort due to an enlarged spleen.

Diagnostic Process

Initial Blood Test: Granulocytosis is most commonly detected during a routine complete blood count (CBC). The CBC measures various components of the blood, and elevated white blood cell counts prompt further investigation.
Differential Count: A lab will perform a differential count to determine which specific type of granulocyte (neutrophil, eosinophil, or basophil) is elevated. This provides crucial clues about the potential cause.
Medical History and Physical Exam: A healthcare provider will review symptoms, recent illnesses, medications, and family history. A physical exam may identify signs like an enlarged spleen.
Further Testing: If initial results and evaluation suggest a more serious condition, additional tests may be ordered. This could include a blood smear, a bone marrow biopsy, or genetic testing to confirm conditions like leukemia.

Treatment and Management

The treatment for granulocytosis is always directed at the underlying cause, not the high count itself. Once the primary condition is addressed, granulocyte levels typically return to normal.

Infections: Bacterial infections are treated with antibiotics, while other infections may resolve on their own.
Autoimmune Disorders: Immunosuppressant medications may be used to calm the immune system and reduce inflammation.
Cancers: Treatment plans for blood cancers can involve chemotherapy, radiation therapy, targeted therapies, or bone marrow transplantation, depending on the specific diagnosis.
Medication-Related Granulocytosis: Discontinuing the causative medication, under a doctor's supervision, will typically resolve the issue.

Granulocytosis vs. Other Blood Conditions

It is important to distinguish granulocytosis from similar-sounding blood conditions to ensure proper diagnosis and treatment. The Cleveland Clinic provides excellent patient resources for comparing and contrasting these conditions.


Condition	What It Is	Key Difference from Granulocytosis
Granulocytosis	An increased number of granulocytes (neutrophils, eosinophils, basophils) in the blood.	Signifies an overproduction of this specific type of white blood cell.
Leukocytosis	An increase in the total white blood cell count.	A broader term; granulocytosis is a specific type of leukocytosis.
Granulocytopenia	A lower-than-normal level of granulocytes.	The opposite of granulocytosis; increases infection risk due to too few granulocytes.
Agranulocytosis	A severe form of granulocytopenia, with extremely low or absent granulocytes.	More severe than granulocytopenia and indicates severe bone marrow failure.

When to See a Doctor

If you receive a CBC result showing elevated granulocyte levels, your doctor will guide you on the next steps. While a mild, temporary increase can be normal in response to an infection, persistent or unexplained high levels, especially alongside concerning symptoms, should not be ignored.

Seek medical attention if you experience:

Persistent, unexplained fatigue
Fever that doesn't go away
Unexplained weight loss
Abnormal bleeding or easy bruising
Pain or swelling in the upper left abdomen
Frequent or persistent infections

Your healthcare provider can assess your overall health and determine if further testing is necessary to pinpoint the exact cause of your granulocytosis.

Frequently Asked Questions

The seriousness of granulocytosis depends on its underlying cause. It can be a harmless, temporary response to an infection, or it could be a sign of a more serious, chronic condition such as a bone marrow disorder or cancer. A doctor's evaluation is necessary for an accurate diagnosis.

Leukocytosis is a broad term for an elevated total white blood cell count. Granulocytosis is a more specific type of leukocytosis, referring only to an increase in granulocytes (neutrophils, eosinophils, and basophils).

Yes, infections are a very common cause of granulocytosis. When the body fights off a bacterial infection, it produces more neutrophils, leading to a temporary rise in the granulocyte count.

Granulocytosis can be categorized based on the specific type of granulocyte that is elevated. For example, a high neutrophil count is called neutrophilia, an elevated eosinophil count is eosinophilia, and a high basophil count is basophilia.

Ignoring granulocytosis can be dangerous because it means the underlying condition is also left untreated. Depending on the cause, this could lead to worsening infections, inflammation, or progression of a blood-related cancer.

Yes, extreme physical or emotional stress, such as from surgery or injury, can cause a temporary increase in granulocyte levels. Lifestyle factors like smoking and poor diet can also contribute to chronic inflammation and elevated granulocyte counts.

Diagnosis begins with a complete blood count (CBC), which reveals an elevated granulocyte level. A doctor will then take a full medical history, conduct a physical exam, and may order further tests like a blood smear or bone marrow biopsy to determine the root cause.