Low levels of basophils in the blood are common in a healthy person. Although, extremely low levels usually indicate an overwhelming shock in the body that is eliminating white blood cells faster than our bodies can produce them (due to severe infection or allergies) or the presence of certain drugs like cancer chemotherapy and corticosteroids. Cancer itself is also known to cause the level of basophils to be too low. In women, pregnancy can sometimes result in an unusually low basophil count. 

An elevated level of basophils in the blood happens in response to infection or inflammation. In the case of infection, a virus is typically the cause. Inflammatory diseases (such as: inflammatory bowel disease & asthma) are known to increase basophil count, and removal of the spleen has the same result. Variations in certain hormones (like thyroid) can also stimulate basophil production. For women, an increase in estrogen is known to elevate basophil concentration. More seriously, an unusually high level of basophils in the blood may indicate cancers of the bone or bone marrow where white blood cells are made like Hodgkin’s Lymphoma and Chronic Myelogenous Leukemia.