Hi Steven,
Hopefully it was not your father's white blood cell count but the type of white blood cells called neutrophils that was 0.5. When the neutrophils are so low many clinics give drugs like Leukine as supportive therapy to their patients.
Your father has to be very careful because he has problems if he should get an infection now. There are many sites about neutropenia and here is one:
http://www.neutropenia.ca/about/living.html
Take care!
Kind regards
Birgitta-A