Absence or decreased number of hematopoietic precursor cells → pancytopenia<unk> , thrombocytopenia, neutropenia)
Causes:
Drug-induced (chloramphenicol, carbamazepine, valproic acid, phenytoin)
Viral infection (parvovirus B19, HIV, hepatitis), especially in patients with sickle cell disease or immunocompromise
Autoimmune
Congenital (Fanconi<unk> 
Drug-induced (chloramphenicol, carbamazepine, valproic acid, phenytoin)
Viral infection (parvovirus B19, HIV, hepatitis), especially in patients with sickle cell disease or immunocompromise
Autoimmune
Congenital (Fanconi<unk>
Aplastic anemia
Acute leukemia
Polycythemia vera
Myelodysplastic syndrome, myelofibrosis
Myelodysplastic syndrome
Myelofibrosis
Infiltrative disease 
Acute myeloid leukemia