A high white blood cell count affects the ability to donate blood, since it is a sign of infection, disease, drug reaction or immune system disorder that must be resolved before donating, state Mayo Clinic and the American Red Cross. Donors with active infections can donate after finishing their antibiotics.
When disease-fighting cells, called leukocytes, increase in the blood, the result is a high white blood cell count, or leukocytosis, notes Mayo Clinic. Bacterial and viral infections, leukemia, and other bone marrow diseases are among the causes of leukocytosis.
Patients who have a fever of 99.5 degrees Fahrenheit or an acute infection cannot donate until the condition has cleared, notes the American Red Cross. As of 2015, the American Red Cross tests every unit of donated blood for many infectious diseases, including hepatitis B and C, syphilis, and Types 1 and 2 of the human immunodeficiency viruses, HIV.