White blood cells play an important role in the immunity/immune system of an individual. The white blood cell count is performed routinely as part of a complete blood count . An unusually high white blood cell count can indicate an infection, hypersplenism , bone marrow depression (drugs, radiation or heavy metal poisoning) or primary bone marrow disorders such as leukemia . A low white blood cell count can be the result of infection, make an individual more susceptible to outside infections or allow multiplication of organisms within the body which would normally kept in check by a healthy immune system.
According to the University of Virginia School of Medicine, a drop in the count of one of the main leukocytes, called neutrophils, is the main sign of low white cell count. This condition is known as neutropenia. Neutrophils are the cells that protect the body from major infections, such as fungal and bacterial infections. However, people without leukopenia can temporarily have all the symptoms of neutropenia if they are sick and the neutrophils temporarily drop. A doctor has to determine whether neutropenia is actually a symptom of a low white blood cell count using a series of tests.