White Blood Cell Differential Count

The white blood cell differential assesses the ability of the body to respond to and fight infection. It can detect the severity of allergic and drug reactions, parasitic and other types of infection. It can also identify some types of leukaemia and lymphoma, and detect other diseases affecting the bone marrow.

The white blood cell differential is automatically run as part of the full blood count (FBC), which is requested for many different conditions. It is a common test that can indicate areas for further investigation.

The results indicate the relative percentage and actual numbers of each type of white blood cell that is present.

Neutrophils can increase in response to bacterial infection, inflammatory disease, steroid medication, or more rarely leukaemia. Decreased neutrophil levels may be the result of severe infection, liver disease, enlarged spleens or other conditions, such as responses to various medications or chemotherapy.

Eosinophils can increase in response to allergic disorders, inflammation of the skin, and parasitic infections. They can also occur in response to some infections or to various bone marrow malignancies.

Basophils can increase in cases of leukaemia, long-standing inflammation, the presence of a hypersensitivity reaction to food, or radiation therapy.

Lymphocytes can increase in cases of bacterial or especially viral infection, leukaemia, lymphoma and in people with underactive or absent spleens. Decreased lymphocyte levels are common in later life but can also be due to steroid medication, stress, lupus, and HIV infection.

Monocyte levels can increase in certain leukaemias, in response to infection of all kinds as well as to inflammatory disorders. Decreased monocyte levels can indicate bone marrow injury or failure and some forms of leukaemia – especially ​“hairy cell leukaemia”.

Age, eating, physical activity, and stress may alter white blood cell differential values. 

Long-term exposure to toxic chemicals (for example some solvents, petroleum products and insecticides) can increase the risk of an abnormal differential as can smoking.

• Neutrophils, the most abundant white blood cells, are ​‘phagocytes’ – that is, they ​‘eat’ foreign organisms and kill them with internal poisons. They are important for fighting bacterial and fungal infections.
• Lymphocytes are more specifically acting killers of infection and regulate the immune response. Some lymphocytes produce antibodies which ​‘remember’ previous infections and guard against re-infection with the same organism. They are active against all types of infection including bacteria, fungi, parasites and viruses. When they malfunction they also have a role in allergy and in autoimmune diseases such as rheumatoid arthritis and lupus.
• Monocytes are phagocytes, like neutrophils, active against bacteria and fungi.
• Eosinophils increase during allergic reactions and some parasitic infestations such as worms.
• Basophils control inflammation and damage to the body. They increase in some blood diseases and in some inflammatory bowel diseases

Neutrophils are also known as granulocytes, polymorphs, and PMNs.