Neutrophils are a type of white blood cell (leukocyte) crucial to the immune system. Produced in the bone marrow, they are the most abundant white blood cell, typically making up 50% to 70% of all white blood cells circulating in the bloodstream. Neutrophils act as a rapid response team, quickly traveling to sites of infection or injury to identify and neutralize foreign invaders such as bacteria and fungi. They combat threats by engulfing and breaking them down, aiding tissue repair and coordinating with other immune cells.
Understanding Neutrophil Levels
When a blood test reveals an increased number of neutrophils, this condition is medically termed neutrophilia. This elevation is identified through a routine Complete Blood Count (CBC) with differential, which measures different cell types. Normal ranges vary by lab, but typically fall between 2,500 and 7,000 neutrophils per microliter for adults, though some labs use 1,500 to 8,000. An elevation above these established ranges suggests the body is actively responding to an underlying stimulus.
Common Causes of High Neutrophils
An elevated neutrophil count often signals the body’s response, with bacterial infections being common triggers. When bacteria invade (e.g., pneumonia, UTIs, skin abscesses), the body rapidly produces and releases more neutrophils to fight pathogens, containing and eliminating the infection.
Beyond infections, various forms of inflammation and tissue injury can also lead to an increase in neutrophil levels. Conditions like rheumatoid arthritis or inflammatory bowel disease, which involve ongoing systemic inflammation, can cause persistent elevations. Physical trauma, including burns, surgical procedures, bone fractures, or even a heart attack, prompts the release of neutrophils to the damaged area to aid in healing and prevent secondary infections.
Temporary increases in neutrophil counts can also occur due to physical and emotional stress. Intense physical exertion, such as vigorous exercise, or psychological stress from anxiety or a panic attack, can trigger a transient rise in these white blood cells. This is part of the body’s adaptation to perceived challenges, mobilizing immune cells even without infection.
Certain medications are known to influence neutrophil levels, with corticosteroids being a primary example. Drugs like prednisone can cause a notable increase in neutrophils by affecting their release from the bone marrow into circulation. Other medications, including granulocyte colony-stimulating factors (G-CSF) or lithium, can also directly stimulate neutrophil production or release, leading to higher counts.
Chronic smoking is another factor that can lead to persistently elevated white blood cell counts, including neutrophils. The constant irritation and inflammation from tobacco smoke triggers an ongoing immune response, leading to a sustained increase in these cells.
When Elevated Neutrophils Indicate a Serious Condition
While many causes of elevated neutrophils are common and temporary, a persistently high count can sometimes point to less frequent, more serious underlying conditions. These include chronic disorders of the bone marrow, which are a group of diseases where the bone marrow produces too many blood cells. Myeloproliferative neoplasms (MPNs) are examples of such conditions, encompassing disorders like chronic myeloid leukemia (CML) and chronic neutrophilic leukemia (CNL).
Abnormal stem cells in the bone marrow undergo mutations, leading to uncontrolled neutrophil production. The elevated count is often sustained at very high levels, and may be accompanied by an enlarged spleen or liver. Additional symptoms like unexplained fatigue, weight loss, or easy bruising may also be present, prompting further investigation to distinguish these serious conditions from more benign causes.
How Doctors Determine the Cause
An elevated neutrophil count serves as an important clue, rather than a definitive diagnosis on its own. Doctors begin their investigation by conducting a thorough physical examination and compiling a detailed medical history, including any recent illnesses, symptoms, or changes in overall health. A comprehensive review of all medications the patient is currently taking is also a standard part of this initial assessment, as certain drugs can influence neutrophil levels.
Follow-up testing is often necessary to pinpoint the underlying cause. This might involve repeating the CBC to observe changes, or ordering a C-reactive protein (CRP) test, as CRP levels rise with inflammation and infection. If a more serious condition is suspected, specialized blood tests, bone marrow examinations, or genetic testing may be performed. Treatment for elevated neutrophils focuses on addressing the underlying condition, rather than directly lowering the count.