Neutrophils are white blood cells - they play an important role in our defense against bacterial infections. 

Normally the number of neutrophils increases to fight off infections, but there are many factors which can cause an increase in neutrophil levels.  These include:

• Smoking
• Inflammation, for example arthritis
• Drugs such as steroids
• A myeloproliferative disorder (most MPDs can cause neutrophilia)
• A myelodysplastic disorder (production of abnormal blood cells)
• Myeloma and monoclonal gammopathy of uncertain significance (diseases of the immune system)

Chronic neutrophilic leukaemia is a disease in which there is a higher than normal number of neutrophils.  However, the causes listed above are all much more likely to cause a high neutrophil count to be present. Chronic neutrophilic leukaemia is very rare, in fact only 140 cases have been described in detail.