Neutrophils: what they are, what they tell you and why we test them

Neutrophils are your most common white blood cells and your first defence against bacteria. Your report shows them on two lines: a percentage and an absolute count. The absolute count is what tells you how many you really have.

Why we test them

When bacteria get into your body, neutrophils are the first to arrive and destroy them. They live only a few hours in the blood, so your bone marrow, the blood factory inside your bones, keeps making new ones.

They are the part of the blood count that reacts fastest to a bacterial infection. They also rise with inflammation, hard exercise or stress.

They matter when they are low too: with fewer neutrophils, your body fights bacteria less well. It is often short-lived, but it needs looking into.

What they tell you, and what they do not

If they are high, your body is reacting to something. It can be an infection or inflammation, but also a hard workout, stress or smoking.

If they are low, a virus you just had or a medicine is often behind it. Some people naturally have lower counts, with no higher risk of infection.

And the percentage alone can mislead, because it moves with your total white count. The number that decides is the absolute count.

That is why they are read together with other tests:

• White blood cells: The total, used to work out the absolute count
• Lymphocytes: Their ratio to neutrophils follows inflammation
• CRP: Whether there is inflammation
• Vitamin B12: If it is low, neutrophils can drop

Normal neutrophil levels

Your report shows neutrophils twice. The percentage (NEU%) says what share of your white cells are neutrophils. The absolute count (NEU#) says how many there really are, usually in x10⁹/L (the same number as x10³/µL, thousands of cells per microlitre of blood).

The lab decides what is normal and prints its limits next to each line. Neutrophils are usually the largest share of your white cells.

Look at the absolute count first. A normal percentage can hide a low absolute count, and the other way round.

In the Rosa report you see the neutrophil percentage next to the rest of your blood count, read together with your white cells.

If your neutrophils are high or low

• High neutrophils: An infection is often behind it, but so are exercise, stress or smoking.
• Low neutrophils: Often after a virus or because of a medicine. Some people naturally have lower counts.

What can skew the result

A few things change the number for a while. It helps to know them before you read it.

• A hard workout: In the hours after hard exercise, neutrophils rise for a short while. Arrive at the blood test rested.
• Strong stress: Acute stress can raise them for a few hours. It does not mean something is wrong.
• A recent infection: A bacterial infection raises them, a virus can lower them. They usually return to normal once you recover.
• Cortisone and other medicines: Cortisone raises them, some medicines lower them. Tell your doctor.
• Smoking: People who smoke often have more neutrophils. After quitting, they usually come down within a year.

When to worry

Talk to your doctor if:

• Your absolute count is below your report’s limit.
• They are low together with haemoglobin or platelets.
• They stay high with no clear reason.
• Your absolute count is below 0.5 x10⁹/L: see a doctor the same day, even if you feel well.
• You have a fever and low neutrophils: see a doctor the same day.
• You have a fever with neutrophils below 0.5, or a fever and you feel confused, breathless or faint: call 112 or go to the emergency department.

With Rosa, neutrophils below 0.5 x10⁹/L (absolute count) are always flagged to a doctor, urgently.

Frequently asked questions

What are neutrophils? They are the most common type of white blood cell. They are the first to arrive where there is a bacterial infection, and they destroy the bacteria.

What are normal neutrophil levels? The lab decides and prints them on your report, next to the result. The absolute count matters most: the percentage alone can mislead.

Are neutrophils and granulocytes the same thing? Almost. Granulocytes are three kinds of white blood cell: neutrophils, eosinophils and basophils. Neutrophils are by far the most common, so the two names are often used as if they were the same.

What is the difference between NEU% and NEU#? NEU% is the percentage: what share of your white cells are neutrophils. NEU# is the absolute count, how many there really are, and it is the one that matters. Some reports print it in x10³/µL rather than x10⁹/L: the numbers are the same.

What is the neutrophil-to-lymphocyte ratio? It is the number of neutrophils divided by the number of lymphocytes. It rises with inflammation, but it has not been shown to tell you more than CRP or the two counts on their own.

How often should they be checked? For people who feel well there is no fixed rule: Rosa measures them twice a year, with the blood count. If they are out of range, show the report to your doctor, who decides whether and when to repeat the test.

Sources

• Fioredda and colleagues, European guidelines on the diagnosis and management of neutropenia in adults and children. HemaSphere, 2023. PMID 37008163
• Newburger and Dale, evaluation and management of patients with isolated neutropenia. Seminars in Hematology, 2013. PMID 23953336
• Merz and colleagues, absolute neutrophil count by Duffy status among healthy Black and African American adults. Blood Advances, 2023. PMID 35994632
• Andersohn and colleagues, systematic review of agranulocytosis caused by non-chemotherapy drugs. Annals of Internal Medicine, 2007. PMID 17470834
• Higuchi and colleagues, current smoking is a reversible cause of a raised white cell count. Preventive Medicine Reports, 2016. PMID 27583199