A variety of systemic illnesses including acute and chronic infections, neoplastic diseases, connective tissue disorders, and storage diseases are associated with hematological manifestations. The hematologic manifestations are the result of the following mechanisms:

• Bone marrow dysfunction :
  
  • Anemia or polycythemia
  • Thrombocytopenia or thrombocytosis
  • Leukopenia or leukocytosis
• Hemolysis
• Immune cytopenias
• Alterations in hemostasis
  
  • Acquired inhibitors to coagulation factors
  • Acquired von Willebrand's disease
  • Acquired platelet dysfunction
• Alterations in leukocyte function
  
  

• Normochromic, normocytic, occasionally microcytic
• Usually mild, characterized by decreased plasma iron and normal or increased reticuloendothelial iron
• Impaired flow of iron from reticuloendothelial cells to the bone marrow
• Decreased sideroblasts in the bone marrow
  
  

• Chronic infection is associated with the anemia of chronic illness.
• Acute infection, particularly viral infection, can produce transient bone marrow aplasia or selective transient erythrocytopenia.
• Parvovirus B19 infection in people with an underlying hemolytic disorder (such as sickle cell disease, hereditary spherocytosis) can produce a rapid fall in hemoglobin and an erythroblastopenic crisis marked by anemia and reticulocytopenia.There may be an associated neutropenia.
• Many viral and bacterial illnesses may be associated with hemolysis.
  

• Viral and bacterial infections can produce leukopenia and neutropenia.
• Neutrophilia with an increased band count and left shift frequently results from bacterial infection.
• Neonates, particularly premature infants, may not develop an increase in white cell count in response to infection.
• Eosinophilia may develop in response to parasitic infections.
  

• Decreased marrow production
• Immune destruction
• DIC