A finding of elevated neutrophils, known as neutrophilia, often appears on a routine Complete Blood Count (CBC) with differential. Neutrophils are the most abundant type of white blood cell (leukocyte) produced in the bone marrow, playing a major role in the body’s immune defense. Neutrophilia means the Absolute Neutrophil Count (ANC) is higher than the established normal range, typically 2,500 to 7,000 cells per microliter of blood in adults, though this varies by laboratory. This elevation signals that the body is actively responding to an internal or external stimulus.
How Neutrophils Fight Infection
Neutrophils are the most abundant type of white blood cell, usually comprising 50% to 75% of the total white blood cell count. They are considered the immune system’s first responders, constantly patrolling the bloodstream for signs of trouble. When a signal of injury or invasion is detected, these cells quickly mobilize to the site of inflammation.
Their primary function is to destroy invading microorganisms, particularly bacteria and fungi, through a process called phagocytosis. They physically engulf the pathogen and then destroy it using a potent chemical arsenal of enzymes and reactive oxygen species stored in their granules. Neutrophils also communicate with other immune cells, helping to amplify the overall inflammatory response.
Acute Causes of Neutrophil Elevation
The most frequent cause of a temporary increase in neutrophil count is an acute bacterial infection. When bacteria invade, inflammatory signals prompt the bone marrow to rapidly release large numbers of neutrophils into the circulation. Common examples include pneumonia, a urinary tract infection, or an acute skin infection.
Localized acute inflammation and tissue damage also trigger this mobilization response. This can occur with severe burns, traumatic injuries, or following major surgery, where the body perceives the damaged tissue as a threat requiring immune intervention. Appendicitis, for instance, is a classic surgical condition associated with a rapid rise in neutrophils.
Physical or emotional stress can also lead to a transient rise in the neutrophil count. Intense exercise, emotional distress, or a severe illness can cause the release of stress hormones like cortisol and epinephrine. These hormones cause neutrophils that were previously “stuck” along the vessel walls (the marginal pool) to move into the main circulation, raising the count without new cell production. Tobacco smoking represents a chronic form of irritation that can also sustain a mild elevation in neutrophil count.
Systemic Conditions Leading to Neutrophilia
A persistent elevation in neutrophils can signal a systemic or chronic underlying condition. Non-infectious inflammatory diseases, where the immune system is continuously activated, are common culprits. Conditions such as rheumatoid arthritis, inflammatory bowel disease, or vasculitis can maintain a state of chronic inflammation that keeps the neutrophil count high.
Certain metabolic disorders create an internal environment that the body interprets as stress or inflammation. For example, diabetic ketoacidosis, a serious complication of uncontrolled diabetes, is frequently associated with neutrophilia. Cushing’s syndrome, a condition involving prolonged high levels of the stress hormone cortisol, also directly stimulates the production and release of neutrophils.
Specific medications are also well-known to cause neutrophilia as a side effect. Corticosteroids, which are powerful anti-inflammatory drugs, are a common example, as they mimic the effect of natural stress hormones, causing neutrophils to shift into the circulation. Rarely, a persistent and very high neutrophil count may indicate a hematologic issue, such as a myeloproliferative neoplasm like Chronic Myeloid Leukemia (CML), where the bone marrow produces blood cells uncontrollably.
Interpreting and Managing High Neutrophil Counts
When a high neutrophil count is detected, the Absolute Neutrophil Count (ANC) is the most clinically meaningful figure, as it represents the total number of circulating cells available to fight infection. A healthcare provider will also examine the differential count, which looks at the proportion of different white blood cell types, to gain a clearer picture. The presence of immature neutrophils, often referred to as a “left shift,” suggests a rapid and acute demand for cells, typical of a serious infection.
To identify the root cause, the doctor will look at the patient’s symptoms and often order additional tests that measure general inflammation. Markers like C-Reactive Protein (CRP) and the Erythrocyte Sedimentation Rate (ESR) can confirm the presence of ongoing inflammation. The management of neutrophilia focuses entirely on treating the underlying cause, not the elevated count itself.
If a bacterial infection is diagnosed, the count will typically return to normal after a course of antibiotics. If the cause is a medication, the provider may adjust the dosage or switch the drug. For chronic inflammatory conditions, management involves controlling the primary disease. Monitoring the ANC over time is often necessary to confirm that the count resolves once the underlying issue is addressed.