A person’s blood is made up of many different types of blood cells. White blood cells, also known as leukocytes, help to fight off infection. Leukocytes are a vital part of the immune system. People who have leukopenia have fewer white blood cells than they should. This makes them more likely to get infections. Leukopenia is a condition where a person has fewer white blood cells in their bloodstream than they should. Leukopenia is diagnosed with a blood test called a complete blood count or CBC.A healthy white blood cell count is between 3,500 and 11,000 white blood cells per microliter. A person with leukopenia may have fewer than 3,500 white blood cells per microliter. White blood cells are made in the bone marrow and are critical for the immune system. Having too few of them means the body is less able to fight off infections and diseases. There are five types of white blood cells. Each helps to protect the body from a different kind of infection: Neutrophils: These make up 55 to 70 percent of total white blood cells. They help fight off fungal and bacterial infections. Lymphocytes: These are the second most common type of white blood cell. They protect the body from viral infections. Basophils: These are the least common type of the white blood cells. They are involved in inflammatory reactions to allergens. Monocytes: These are the largest of the white blood cells. They play a role in fighting off bacteria, fungi, and viruses. They also help mend tissue that has been damaged by inflammation. Eosinophil’s: These fight parasites and play a role in allergic reactions and conditions, such as asthma. There are five kinds of leukopenia, each one corresponding to the type of white blood cell that is affected.