Blood smear

An examination of a peripheral blood smear is an essential step in obtaining an ITP diagnosis by excluding other diseases or causes of thrombocytopenia, such as¹:
o HIV infection
o Systemic lupus erythematosus
o Lymphoproliferative disorders
o Myelodysplasia
o Agammaglobulinemia or hypogammaglobulinemia
o Drug-induced thrombocytopenia
o Alloimmune thrombocytopenia
o Congenital/hereditary nonimmune thrombocytopenia

A blood smear of an ITP patient1

Consistent with the diagnosis of ITP

o Platelets are normal in size or may appear larger than normal, but consistently giant platelets (approaching the size of red blood cells) should be absent

o Normal red blood cell morphology

o Normal white blood morphology

Not consistent with the diagnosis of ITP

o Predominant giant platelets

o Red blood cell poikilocytosis, schistocytes, polychromatophilia (unless response to bleeding), macrocytes, nucleated red blood cells

o Leukocytosis or leukopenia, with immature or abnormal cells (although atypical lymphocytes and eosinophilia may occur in children with ITP)

References