Neutrophils are the most numerous group of white blood cells and the first line of defense against bacteria. It is they that arrive first at the site of inflammation.
So a rise in neutrophils is a classic sign of a bacterial infection, and their ratio to lymphocytes (the NLR index) has in recent years been studied as a marker of inflammation and prognosis.
Reference ranges
Both the proportion (%) and the absolute number are assessed; typical values:
| Proportion of white cells | 40 – 70% |
| Absolute number | 1.8 – 7.5 ×10⁹/L |
| Neutrophilia (increase) | bacterial infection, inflammation, stress |
| Neutropenia (decrease) | viruses, medications, bone marrow |
What an elevated level means
A rise in neutrophils (neutrophilia) is most often a bacterial infection or acute inflammation. Also raising it: physical and emotional stress, smoking, glucocorticoids, a heart attack and other tissue damage.
A very high level with "young" forms (a left shift) indicates marked activation and needs a doctor's assessment.
What a low level means
A fall in neutrophils (neutropenia) weakens defense against bacteria.
Causes: viral infections, the use of a number of medications (chemotherapy, some antibiotics, antithyroid drugs), autoimmune processes, B12/folate deficiency, bone-marrow suppression. Marked neutropenia is a risk of severe infections and a reason for urgent assessment.
How the test is done
Neutrophils are measured in the differential count of the complete blood count. No special preparation is required, but stress and exertion before the draw can temporarily raise the result.
They are interpreted together with the total white-cell number, the rest of the differential and, with inflammation, with CRP.
What affects the value
- Bacterial infections and inflammation — raise them.
- Stress and physical exertion — temporarily raise them.
- Glucocorticoids and smoking — raise them.
- Viruses — often lower them.
- Chemotherapy and a number of medications — lower them.
- B12/folate deficiency — can lower them.
Biological age from a blood test
White-cell parameters are part of the PhenoAge biological-age model:
Frequently asked questions
Neutrophils are high — is it a bacterial infection?
Most often yes: neutrophils are the first to respond to bacteria. But a rise also occurs with stress, physical exertion, smoking and glucocorticoid use. The result is assessed together with symptoms and CRP.
What is the NLR (neutrophil/lymphocyte) index?
It is the ratio of neutrophils to lymphocytes — a simple measure of systemic inflammation. An elevated NLR is linked to a more severe course of infections and a worse prognosis in a number of diseases, so it is used as an additional guide.
What is the danger of low neutrophils?
Marked neutropenia reduces defense against bacteria and raises the risk of severe infections. If neutrophils are low, it is important to establish the cause (virus, medication, bone marrow) and, with deep neutropenia, to take precautions.
Related terms
Sources
- Normal and Abnormal CBC with Differential — StatPearls (NCBI)
- MedlinePlus (NIH) — Blood Differential Test
- MedlinePlus (NIH) — Neutrophils (Absolute)