Neutrophils contain primary and secondary granules. The primary granules are azurophilic (Burgundy-coloured) and contain toxic mediators such as elastase and myeloperoxidase. The secondary granules are pink-staining and contain proteins such as lactoferrin; these are not usually visible by light microscopy.

Neutrophilia is the presence of increased circulating neutrophils, and is a common finding in the full blood count of acutely unwell patients.

Acute stress or exertion can cause shift of neutrophils into the circulation, resulting in pseudoneutrophilia. Corticosteroids may cause neutrophilia through demargination of neutrophils from the endothelial lining, delayed migration from the circulation into tissues and delayed apoptosis. After splenectomy patients will develop neutrophilia.

Myeloproliferative disorders are a less common cause of neutrophilia that are important not to miss.

Neutropaenia refers to reduced circulating neutrophils.

Neutropaenia confers increased risk of infections - particularly bacterial and fungal - and fevers in these patients (febrile neutropaenia) are medical emergencies that require prompt investigation and treatment.

Bone marrow pathologies tend to cause pancytopaenia more commonly than isolated neutropaenia, as does cytotoxic chemotherapy. Other medications may cause dose-related or idiosyncratic neutropaenia.

Any condition that induces hypersplenism (including cirrhosis, certain infections, myeloproliferative disorders and chronic haemolytic anaemia), can cause sequestrational loss of neutrophils. Felty's syndrome is the triad of rheumatoid arthritis, splenomegaly and neutropaenia, and is associated with poorer prognosis in the RA patient. Other autoimmune conditions such as SLE may also cause neutropaenia and should be considered.

There are many congenital syndromes that cause chronic neutropaenia; these range from benign to severe and progressive.

This finding is characteristic of megaloblastic anaemia, though may also occur with myelodysplastic syndrome.

Levels of toxic granulation are highly correlated with C-reactive protein (CRP) values in patients with infection or inflammation.

The presence of vacuoles within neutrophils on a blood film is highly suggestive of infection.

Dohle bodies are blue cytoplasmic inclusions seen within neutrophils. These inclusions are remnants of the rough endoplasmic reticulum, and may be seen in cases of significant stress.