Leukopenia

Leukopenia means a white blood cell count below the normal range, usually under about 4,000 cells per microliter in adults. It is most often caused by a low neutrophil count (neutropenia) or a low lymphocyte count (lymphopenia). Common causes include viral infections, medicines such as chemotherapy, some antibiotics, antithyroid drugs and immune-suppressing medicines, autoimmune diseases such as lupus, an enlarged spleen, vitamin B12 or folate deficiency, and bone marrow disorders. Some healthy people, particularly those of African or Middle Eastern descent, have a lower white count that is normal for them. Leukopenia itself causes no symptoms, but a low count can raise the risk of infection.

Lab tests linked to leukopenia:

• White blood cells: the total white cell count. It shows leukopenia is present, but not which type of white cell is low.
• Doctors look at the differential, especially the absolute neutrophil and lymphocyte counts, and a blood smear. They may add a repeat CBC, vitamin B12 and folate, HIV and hepatitis tests, autoimmune tests and, if the cause isn't clear or other blood counts are low, a bone marrow test.

How results are read:

• The absolute neutrophil count matters most for infection risk. A low white count with a normal neutrophil count is usually less concerning.
• A short-lived drop after a viral infection is common and recovers on repeat testing.
• Leukopenia together with low red cells or platelets is a reason for prompt assessment of the bone marrow.
• Reference ranges vary by lab and ancestry.

When to see a doctor:

• See a doctor about a low white count on more than one test, or about frequent or slow-healing infections.
• Get emergency care for a fever of 100.4°F (38°C) or higher if you have a very low neutrophil count or are having chemotherapy.

Clinical takeaway: leukopenia is confirmed on the white cell count, and the differential and repeat testing show which cells are low and whether the cause needs further tests.