Blood Differential Test

A blood differential test measures the amount of each type of white blood cell in your blood. It helps diagnose or monitor infections, autoimmune diseases, and conditions affecting your immune system.

What this test measures

A blood differential test measures the amount and/or percentage of each type of white blood cell (neutrophils, lymphocytes, monocytes, eosinophils, and basophils) in your blood.

What your results mean

Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.

Higher-than-normal results

According to MedlinePlus, a high white blood cell count (leukocytosis) may be caused by infections, autoimmune or inflammatory disorders, leukemia, Hodgkin disease, allergic reactions, or certain steroids.

Lower-than-normal results

According to MedlinePlus, a low white blood cell count (leukopenia) may be caused by bone marrow diseases, chemotherapy, certain medicines (such as antibiotics), cancer, or HIV.

Frequently asked questions

What is a blood differential test?

It measures the amount of each type of white blood cell in your blood to help diagnose or monitor infections and immune system conditions.

What are the five types of white blood cells?

Neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

What can cause a high white blood cell count?

Infections, autoimmune disorders, leukemia, allergic reactions, or certain steroids.

What can cause a low white blood cell count?

Bone marrow diseases, chemotherapy, certain medicines, cancer, or HIV.

Do abnormal results always mean I have a medical condition?

No, abnormal results can also be due to physical injury, stress, smoking, or alcohol use. Your provider will consider other factors.

Sources

MedlinePlus: Blood Differential — NIH MedlinePlus

Last updated July 7, 2026. Information is aggregated from official public sources and is not a substitute for professional medical care.