Neutrophils are a type of white blood cell that acts as the immune system’s first line of defense. They are the most abundant white blood cell, making up 50-70% of the total count. When your body detects an infection or sustains an injury, neutrophils are the initial responders to arrive at the scene.
Produced in the bone marrow, these cells circulate throughout your bloodstream. Upon receiving chemical signals from a site of injury or infection, they travel to the area to perform their primary function: engulfing and digesting invaders like bacteria. This process is known as phagocytosis, and the resulting inflammation, like redness and swelling, shows that neutrophils are working to neutralize threats.
Understanding Neutrophilia
The medical term for a high count of neutrophils is neutrophilia, which signifies that the percentage of these cells in the bloodstream has risen above the normal range. This is identified through a complete blood count (CBC), a routine test that measures blood components. A “differential” is often included with a CBC to specify the percentage of each type of white blood cell.
For most adults, a normal absolute neutrophil count falls between 2,500 and 7,500 neutrophils per microliter of blood. A count exceeding 7,500 per microliter is considered neutrophilia.
These reference values are not universal, as the specific numbers defining a normal or high count can vary. Differences depend on the laboratory conducting the test, as well as an individual’s age and other factors. A result flagged as “high” is a clinical indicator that prompts further evaluation.
Common Causes of Elevated Neutrophils
The most frequent reason for an elevated neutrophil count is the body’s response to a bacterial infection. The immune system ramps up production of neutrophils in the bone marrow and releases them into the bloodstream to fight the invaders. This surge is a normal reaction, indicating your immune defenses are working to resolve the infection.
Inflammation unrelated to infection is another common trigger. This can occur after a physical injury, such as a broken bone, or following a surgical procedure. Inflammatory conditions like gout, which involves uric acid crystals in joints, can also cause a temporary spike in neutrophil levels as the body attempts to clear them.
Certain medications are known to increase neutrophil counts. Corticosteroids, such as prednisone, are a primary example. These drugs cause neutrophils settled along blood vessel walls to move into circulating blood, which inflates the numbers on a blood test. This effect is temporary and resolves once the medication is discontinued.
Physiological stress can also lead to a temporary rise in neutrophils. Intense physical exertion, significant emotional distress, or pregnancy can signal the body to release more of these white blood cells. Additionally, lifestyle habits like smoking are linked to chronically elevated neutrophil levels due to constant lung irritation, which keeps the immune system on high alert.
Serious but Less Common Causes
While most cases of high neutrophils are temporary, the finding can sometimes point to more significant health conditions. Chronic inflammatory diseases are one such category. Conditions like rheumatoid arthritis or inflammatory bowel disease (IBD) can lead to persistently elevated neutrophil levels due to the ongoing inflammation they produce.
In some instances, a high neutrophil count can indicate certain blood disorders or cancers. For example, chronic myeloid leukemia (CML) is a cancer that begins in the bone marrow and leads to the overproduction of white blood cells, including neutrophils. Such causes are far less common than infections or inflammation.
When a serious condition is the cause, the elevated neutrophil count is rarely the only abnormal finding. Patients often experience other symptoms, such as fatigue, unexplained weight loss, or persistent fevers. Blood tests would also likely reveal other abnormalities, which helps guide a physician toward a more specific investigation.
When to See a Doctor
A high neutrophil count is a finding that requires interpretation by a healthcare professional; it is not a standalone diagnosis. The number is a piece of a larger puzzle, and its significance can only be understood in the context of your overall health and medical history. You should always discuss any abnormal lab results with your doctor.
A physician will evaluate the neutrophilia by considering potential causes, such as a recent infection, injury, or new medication. They will ask about any symptoms you may be experiencing, like fever, pain, or fatigue, to help determine the underlying reason. This review is necessary to understand what the lab value means for you.
Depending on the clinical picture, your doctor may repeat the complete blood count at a later date. This helps determine if the elevation was transient or if it is persistent, which might suggest an ongoing issue. If inflammation is suspected but the cause is unclear, other tests like a C-reactive protein (CRP) test may be ordered to confirm its presence.