Page 3
Complete blood count (CBC)
Isolated thrombocytopenia is typically associated with immune-mediated disorders (e.g. ITP, DITP) and inherited disorders (e.g. Bernard-Soulier, TAR syndrome), but is uncommon in malignant processes involving bone marrow. Thrombocytopenia associated with anemia and leucopenia (pancytopenia) can be caused by bone marrow suppression by various medications (commonly chemotherapy, rarely antihypertensive medications and antibiotics e.g. chloramphenicol); viral infections (HIV); bacterial infections (e.g. leishmaniasis); severe folate and B12 deficiency; paroxismal nocturnal hemoglobinuria; systemic lupus erythematosus (SLE); inherited disorders (e.g. dyskeratosis congenita, Fanconi anemia); malignancy (metastatic disease, leukemia, lymphoma with bone marrow involvement, multiple myeloma, rarely solid tumors) or bone marrow failure (e.g. aplastic anemia, myelodysplastic syndrome) If thrombocytopenia is associated with neutrophilia, infection should be considered or, rarely, chronic myeloid leukemia, usually associated with “left shift” — an increased percentage of immature neutrophils (bands, metamyelocytes and myelocytes). Thrombocytopenia can be accompanied by lymphocytosis suggestive of lymphoid malignancies (e.g. chronic lymphocytic leukemia [CLL], pertussis, or viral infections). Blood smear has inestimable value in the diagnosis of thrombocytopenia. Firstly, as discussed, pseudothrombocytopenia should be excluded. Secondly, in cases of true thrombocytopenia, blood cell morphology should be investigated thoroughly. Giant platelets can be found with different types of hereditary thrombocytopenia (Paris-Trousseau thrombocytopenia, gray platelet syndrome, Bernard-Soulier) and these can result in falsely low platelet counts if the giant platelets are not counted as platelets. Microthrombocytes are typically seen in WAS or X-linked thrombocytopenia and TORCH infections (toxoplasmosis, others [such as syphilis, varicella-zoster, parvovirus B19], rubella, cytomegalovirus, and herpes infections). Neutrophils with toxic granulation occur in blood smears of patients with sepsis, and Döhle-like bodies in the cytoplasm of neutrophils are seen in the MYH9-related disorders (May-Hegglin anomaly associated with MYH9 gene). Neutrophils with bilobed nuclei suggest Pelger-Huèt anomaly. Atypical lymphocytes are seen in many viral infections in children but Epstein-Barr virus is the one classically associated with type II atypical lymphocytes or Downey cells.