A 20 year old male complains of recurrent attacks of sore throat since 2 years. The total leukocyte count was 1000/μl. A differential count revealed severe neutropenia. The diagnosis is:
A reduction in the number of granulocytes in blood is known as neutropenia or, when severe, agranulocytosis.
Neutropenic persons are susceptible to severe, potentially fatal bacterial and fungal infections. 
The risk of infection rises sharply as the neutrophil count falls below 500 cells/μL.

Kumar V, Abbas AK, Aster JC. Robbins basic pathology. Elsevier Health Sciences; 2017. Page 459
Subleukemic leukemia
Infectious mononucleosis
Agranulocytosis
Leukoerythroblastic anemia