What Does Low WBC in a Blood Test Mean?

Q: What Does Low WBC in a Blood Test Mean?

Low WBC (leukopenia) explained: below 4,000/µL, causes including viral infection, chemotherapy, autoimmune disease, and when low WBC increases infection risk.

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

Source: NLM MedlinePlus, American Association for Clinical Chemistry.

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