What are the possble causes of a 13 month old baby having low blood count (4.5)? she has been exceptionally healthy until ear infection, flu 3 weeks ago

Virus induced: Viruses can cause a low white count. Its just a transient thing. Not to worry.

Lab tests: Several possibilities, but best to discuss this with the pediatrician who ordered the cbc.

WBC count: The differential of the white blood cell count is an important part of the testing. If she is otherwise acting normally, eating well and without fever, a follow up ear examination may be performed at 2-3 weeks from diagnosis. If there is concern for an illness, the CBC, differential and platelet count may be repeated.