What Does Low WBC in a Blood Test Mean?

Low WBC (below 4,000/µL) is called leukopenia. It means your immune system has fewer defenders than normal.

Common Causes

• Viral infection — many viruses temporarily suppress WBCs
• Chemotherapy — bone marrow suppression
• Autoimmune disease — lupus
• Certain medications
• HIV/AIDS
• Severe malnutrition

Infection Risk

• Above 2,000: generally normal defense
• 1,000–2,000: moderate risk
• Below 500: high risk — febrile neutropenia is an emergency