Neutrophils
The most numerous white blood cell and the body's first responder to bacterial infection. A high count usually means infection, inflammation or stress; a very low count (neutropenia) leaves the body vulnerable to serious infection.
What it measures
Neutrophils are the most common type of white blood cell and the frontline of the immune system's response to bacterial and fungal infection — they are the first cells rushed to a site of infection to engulf and destroy microbes. They are reported as part of the full blood count differential, both as a percentage and, more usefully, as an absolute count. Because they respond quickly and in large numbers, a raised neutrophil count is one of the commonest lab signs of an acute bacterial infection, but it also rises with inflammation, tissue injury, physical or emotional stress, smoking and steroid medication. A low count matters in the opposite way: too few neutrophils (neutropenia) weakens defence against infection, and a very low count is a medical concern, most often after chemotherapy.
What a high value can mean
- Bacterial infection — the classic cause; often with a raised CRP.
- Inflammation or tissue damage — injury, surgery, burns, inflammatory disease.
- Physical or emotional stress, vigorous exercise — a rapid, temporary rise.
- Steroid medication (corticosteroids).
- Smoking.
- Rarely — a bone-marrow disorder such as chronic myeloid leukaemia (very high counts).
What a low value can mean
- Neutropenia — too few neutrophils; raises infection risk.
- After chemotherapy or radiotherapy — the commonest serious cause.
- Viral infections — can transiently lower neutrophils.
- Certain medications, autoimmune conditions, B12/folate deficiency.
- Ethnic benign neutropenia — a lower baseline in some healthy people, not a problem.
When to discuss with a doctor
A modestly raised neutrophil count with symptoms of infection usually fits the clinical picture and is managed by treating the infection. The count that demands attention is a low one: significant neutropenia — especially after chemotherapy — with a fever is a medical emergency (neutropenic sepsis), because the usual signs of infection may be blunted and it can progress fast. Anyone on chemotherapy with a fever should seek urgent care. A persistently abnormal count without an obvious cause is investigated further. Mediora.AI shows the neutrophil count within the white-cell differential alongside CRP so the infection/inflammation pattern is visible; the clinical decision belongs with your doctor.