High neutrophils (neutrophilia): what it means and why it happens

Neutrophils are measured as part of a full blood count and its white blood cell differential. Lab Tests Online UK describes them as the most abundant white blood cells and as phagocytes, cells that engulf and kill foreign organisms. They are important for fighting bacterial and fungal infections. They may appear on a lab report as granulocytes, polymorphs or PMNs.

When the count is above the reference range, the finding is called neutrophilia. Lab Tests Online UK says a high count usually suggests bacterial infection, inflammation or physical stress on the body. In other words, it is most often a sign that the body is responding to something, rather than a disease of the blood itself.

Because the result is read alongside the other white cell types, red cells and platelets, a single raised figure rarely means much on its own. Your doctor will interpret it in the context of your symptoms, age, sex, medical history and, as Lab Tests Online UK stresses, your ethnic background, because normal neutrophil levels differ between ethnic groups.

The white blood cell differential page lists the main reasons neutrophils can increase: bacterial infection, inflammatory disease, steroid medication or, more rarely, leukaemia. Lab Tests Online UK adds that a high white cell count in general can indicate infection, inflammation, or leukaemia and other blood disorders.

Temporary and everyday factors matter too. Lab Tests Online UK says age, eating, physical activity and stress can alter white cell differential values, and that long-term exposure to toxic chemicals, such as some solvents, petroleum products and insecticides, and smoking can increase the risk of an abnormal differential. A blood test taken while you are acutely unwell, after strenuous exercise or after a steroid course will often show a higher count that settles by itself.

• Bacterial infection, such as a chest, urine or skin infection.

• Inflammatory conditions.

• Steroid medicines, including tablets and some injections.

• Physical stress, such as recent surgery or injury.

• Smoking.

• Less commonly, blood disorders such as leukaemia.

High neutrophils do not cause symptoms by themselves. Any symptoms come from the underlying cause, for example fever, a cough, painful urination, a hot swollen area of skin or joint pain. If you have symptoms of infection, the most appropriate route depends on severity. For an illness that is not improving or is getting worse, contact your GP or NHS 111.

Seek urgent help through NHS 111 or 999 if you feel severely unwell, are confused or have difficulty breathing. Tell anyone treating you if you take steroids or have had chemotherapy, because these change how blood counts should be read.

Lab Tests Online UK explains that many results slightly outside the normal range do not need treatment, and your doctor may repeat the test after a short period to see whether the result has changed. If the white cell count is significantly raised, further tests may look for infection, bone marrow problems or blood disorders.

It lists a blood film, in which the cells are looked at under a microscope, as often used alongside the full blood count to give more information. A doctor will also ask about symptoms and review the medicines you take, since Lab Tests Online UK notes that many drugs can raise or lower white cell counts. Referral to haematology is generally reserved for counts that are very high, persistent without explanation, or accompanied by other abnormal cell lines.

A low neutrophil count, called neutropenia, has a different set of causes and implications. Lab Tests Online UK says it raises your risk of infection, and the differential page lists severe infection, liver disease, enlarged spleens, medicines and chemotherapy among its causes. A high count is almost the opposite in meaning: the body is typically mounting a response to something. The related guide on low neutrophils covers that scenario.

Full blood counts are routinely requested by GPs and hospital doctors. Results are reviewed in context, and repeat tests are done in primary care. Private blood tests are available in the UK, but an abnormal white cell result should be discussed with a clinician who knows your history, as the same number can mean different things in different people.