What Causes Elevated Neutrophil Levels?

Elevated neutrophil levels, also known as neutrophilia, occur when the body produces an unusually high number of neutrophils—white blood cells that play a crucial role in fighting infections. Neutrophils are the most abundant type of white blood cell in the bloodstream, accounting for 50% to 70% of all circulating leukocytes. On average, these cells survive in the bloodstream for about 5.4 days before migrating into tissues, where they respond rapidly to sites of infection or injury.

Common Causes of Neutrophil Increase

One of the primary reasons for elevated neutrophil counts is infection. Bacterial infections are particularly likely to trigger a significant rise in neutrophils, but fungal, parasitic, and certain viral infections can also lead to mild or moderate increases. When pathogens invade the body, the immune system signals the bone marrow to release more neutrophils to combat the threat, resulting in higher-than-normal levels detected in blood tests.

Tissue Damage and Inflammation

Significant physical trauma or tissue destruction is another major contributor to neutrophilia. Conditions such as severe injuries, major surgical procedures, extensive burns, or areas of tissue necrosis (cell death) prompt the body to initiate an inflammatory response. This process involves the rapid mobilization of neutrophils to the affected area, which in turn elevates their concentration in the bloodstream.

Neutrophilia Linked to Cancer

Abnormally high neutrophil levels can also be associated with certain types of cancer. Tumors in the gastrointestinal tract or lungs—especially cases involving metastatic lung cancer spreading to the liver—have been observed to cause neutrophilia. In some instances, cancerous growths produce substances that stimulate excessive production of white blood cells, including neutrophils, as part of a paraneoplastic syndrome.

Normal Neutrophil Count Ranges

The total neutrophil count is typically included in a complete blood count (CBC) test and is often interpreted alongside the overall white blood cell count. For most healthy adults—both men and women—the normal range for white blood cells is between 4.0 and 10.0 × 10⁹/L. However, newborns have naturally higher levels due to their developing immune systems, with reference values ranging from 15.0 to 20.0 × 10⁹/L during the first few days of life.

Understanding what drives elevated neutrophil levels is essential for accurate diagnosis and treatment planning. While temporary increases are often a sign of the body's natural defense mechanisms at work, persistently high counts may indicate underlying health issues that require further medical evaluation.