Not medical advice: It is called "Leukopenia", a term used for low, decrease or deficiency of white blood cell (leukocytes) count. When you have a low white blood cell (WBC) count you may be immunosuppressed, which means you are more at risk for potentially serious infections that do not go away or are hard to treat. In most cases it is due to low lymphocytes (lymphocytopenia) and/or neutrophils (neutropenia). Both of these cell types play a big role in the body’s defense against infections.
Infections like viral infections, autoimmune disorders such as lupus, certain medications (including chemotherapy and some antibiotics), radiation therapy, and bone marrow illnesses (such as leukemia or myelodysplastic syndromes) can lead to decreases in neutrophils and/or lymphocytes.
Of interest, researchers at the University of British Columbia have developed a new way to detect blood doping using DNA, white blood cells are inspected for different populations of genes using PCR (polymerase chain reaction). Find out more at UBC.