Chemotherapy, and radiation therapy are the other causes. Other common causes of
low WBC are flu, lupus, Hodgkin's lymphoma, some types of
cancer, typhoid, malaria, tuberculosis, dengue, enlarged spleen or hyper-spleenism, and folate deficiency. Please discuss with his treating doctor to run tests to find the cause. If all these are ruled out, then it can be bone-marrow suppression. So, if you recently had fever, then its better to wait for some time and then repeat the test. Take care!