White Blood Cells (WBC / Leukocytes)

What are White Blood Cells?

White blood cells, also called leukocytes or WBCs, are the soldiers of your immune system. Unlike red blood cells that carry oxygen, white blood cells defend your body against infections, viruses, bacteria, and other foreign invaders.

Your bone marrow produces white blood cells, which then circulate through your blood and lymphatic system, ready to respond to threats.

A complete blood count (CBC) measures your total white blood cell count and can break it down into different types, each with specific roles.

Normal Ranges

Marker	Normal Range
Total WBC	4,000–11,000 cells/µL
Neutrophils	40–70% of WBC
Lymphocytes	20–40% of WBC
Monocytes	2–8% of WBC
Eosinophils	1–4% of WBC
Basophils	0–1% of WBC

Types of White Blood Cells

Neutrophils

The first responders. They attack bacteria and fungi. Elevated neutrophils often indicate bacterial infection.

Lymphocytes

Include T cells, B cells, and natural killer cells. They handle viruses, coordinate immune responses, and create antibodies.

Monocytes

The cleanup crew. They engulf dead cells and pathogens, and become macrophages in tissues.

Eosinophils

Rise during allergic reactions and parasitic infections.

Basophils

Involved in allergic and inflammatory responses. The rarest type.

Why It Matters

Infection Detection

Elevated WBC often indicates your body is fighting an infection. The pattern of elevation (which cell types are high) helps identify the type of infection.

Immune System Health

Low WBC counts may indicate immune suppression from medications, viral infections, or bone marrow problems.

Chronic Disease Monitoring

Conditions like autoimmune diseases, leukemia, and other blood disorders affect white blood cell counts and distribution.

High vs. Low WBC

High WBC (Leukocytosis)

Bacterial infections
Inflammation
Stress response
Certain medications (steroids)
Rarely: leukemia