Leukocyte Count with Differential (Cell Count)

Why This Test Is Done

Doctors order a WBC differential when they suspect an infection (such as pneumonia, urinary tract infection, or bloodstream infection), evaluate immune system function, check for signs of inflammation, or monitor conditions like leukemia, lymphoma, or autoimmune diseases. It may also be done before surgery or during chemotherapy to monitor how well your body is handling treatment.

What to Expect Before the Test

No special preparation is needed for this test. You may have a small needle inserted into a vein in your arm or hand to draw blood. If you’re nervous, let your healthcare provider know—they can help make the process more comfortable. Avoid eating or drinking for a short time before blood draws if instructed, but this is not always required for a WBC differential.

What Happens During the Test

A healthcare professional will clean the area with an antiseptic, insert a small needle into your vein, and collect a small amount of blood. The blood sample is then sent to a lab where it is analyzed under a microscope to count and identify each type of white blood cell. The results are usually available within a few hours or the next day.

What the Results Mean

The test provides a breakdown of your total WBC count and the proportion of each type. For example, high numbers of neutrophils may indicate an infection, while high lymphocytes could suggest a viral infection or immune response. Low counts of certain cells might signal immune deficiencies or other health issues. Your doctor will interpret the results in the context of your symptoms and medical history.