Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (292 page)

   Laboratory Findings

   CBC: Moderate anemia, normal to slightly reduced MCV in inflammatory conditions; normal red cell morphology, with only mild variation in RDW. In anemia of chronic renal failure, burr cells can be seen on the peripheral blood smear (PBS).

   Inadequate reticulocyte response.

   Increased serum ferritin; reduced serum iron and TIBC.

   Serum erythropoietin is inadequate for the level of anemia, especially in renal failure.

APLASTIC ANEMIA (AA)

   Definition

Although the name refers only to anemia, AA is characterized by peripheral blood pancytopenia. It is the paradigm of bone marrow failure. The diagnosis of AA is one of exclusion. There is variable bone marrow hypocellularity due to diminished or absent hematopoietic precursors, the result of injury to the pluripotent stem cell. The absence of a myeloproliferative neoplasm or an MDS is a prerequisite for the diagnosis.

   Etiology

   AA may be acquired or congenital (Fanconi anemia; see below). More than 50% of the acquired cases are idiopathic, most likely due to an autoimmune mechanism that destroys or suppresses the hematopoietic stem cell via cytotoxic T lymphocytes and the cytokines they produce.

   Other cases may result from drugs, such as chemotherapy, anticonvulsants, and many more. It is essential to obtain a history of drug or toxin exposure.

   Immunologic disorders such as graft versus host disease.

   Thymomas.

   Exposure to ionizing radiation.

   Viral infections: EBV and the putative agent of seronegative hepatitis.