decrease in white blood cell count. The FDA monograph for metronidazole states that this medication can also cause leukopenia, and the prescriber information suggests a complete blood count, including differential cell count, before and after, in particular, high-dose therapy. Immunosuppressive drugs, such as sirolimus, mycophenolate mofetil, tacrolimus, ciclosporin, leflunomide and TNF inhibitors, have leukopenia as a known complication. Interferons used to treat multiple sclerosis, such as interferon beta-1a and interferon beta-1b, can also cause leukopenia. Chemotherapy targets cells that grow rapidly, such as tumors, but can also affect white blood cells, because they are characterized by bone marrow as rapid growing. A common side effect of cancer treatment is neutropenia, the lowering of neutrophils (a specific type of white blood cell). Decreased white blood cell count may be present in cases of arsenic toxicity. Diagnosis Leukopenia can be identified with a complete blood count. Below are blood reference ranges for various types leucocytes/WBCs. The 2.5 percentile (right limits in intervals in image, showing 95% prediction intervals) is a common limit for defining leukocytosis. References External links Blood disorders