White Blood Cell Differential Count (with Absolute Counts)

What Is a White Blood Cell Differential?

A white blood cell differential (or WBC differential) breaks down the five main types of white blood cells (neutrophils, lymphocytes, monocytes, eosinophils, and basophils) into percentages and sometimes absolute counts. This helps determine if your immune system is responding normally or if an infection, allergy, or other condition is affecting your blood.

Why Might You Need This Test?

Doctors order a WBC differential when they suspect an infection (like pneumonia or sinusitis), an autoimmune disorder (such as lupus or rheumatoid arthritis), a blood disorder (like leukemia), or an allergic reaction. It can also be used to monitor chronic conditions like asthma or inflammatory bowel disease.

How Is the Test Performed?

A small blood sample is taken from a vein, usually in your arm. The sample is sent to a lab, where it’s examined under a microscope to count and identify the different types of white blood cells. Some labs may also calculate absolute counts (the actual number of each type per microliter of blood).

What Does the Test Result Mean?

Results show percentages of each white blood cell type, along with absolute counts if provided. For example, a high neutrophil count might suggest bacterial infection, while a high lymphocyte count could indicate a viral infection or chronic illness. Abnormal results don’t always mean a problem exists—your doctor will interpret them in the context of your symptoms and medical history.